Method to construct 3d devices and systems

ABSTRACT

A method to construct a 3D system, the method including: providing a base wafer; transferring a first memory wafer on top of the base wafer; thinning the first memory wafer, thus forming a thin first memory wafer; transferring a second memory wafer on top of the thin first memory wafer; thinning the second memory wafer, thus forming a thin second memory wafer; and transferring a memory control wafer on top of the thin second memory wafer; where the transferring a memory control wafer includes bonding of the memory control wafer to the thin second memory wafer, and where the bonding includes oxide to oxide and conductor to conductor bonding.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This application relates to the general field of Integrated Circuit (IC)devices and fabrication methods, and more particularly to multilayer orThree Dimensional Integrated Memory Circuit (3D-Memory) and ThreeDimensional Integrated Logic Circuit (3D-Logic) devices and fabricationmethods.

2. Discussion of Background Art

Over the past 40 years, there has been a dramatic increase infunctionality and performance of Integrated Circuits (ICs). This haslargely been due to the phenomenon of “scaling”; i.e., component sizessuch as lateral and vertical dimensions within ICs have been reduced(“scaled”) with every successive generation of technology. There are twomain classes of components in Complementary Metal Oxide Semiconductor(CMOS) ICs, namely transistors and wires. With “scaling”, transistorperformance and density typically improve and this has contributed tothe previously-mentioned increases in IC performance and functionality.However, wires (interconnects) that connect together transistors degradein performance with “scaling”. The situation today is that wiresdominate the performance, functionality and power consumption of ICs.

3D stacking of semiconductor devices or chips is one avenue to tacklethe wire issues. By arranging transistors in 3 dimensions instead of 2dimensions (as was the case in the 1990s), the transistors in ICs can beplaced closer to each other. This reduces wire lengths and keeps wiringdelay low.

There are many techniques to construct 3D stacked integrated circuits orchips including:

-   -   Through-silicon via (TSV) technology: Multiple layers of dice        are constructed separately. Following this, they can be bonded        to each other and connected to each other with through-silicon        vias (TSVs).    -   Monolithic 3D technology: With this approach, multiple layers of        transistors and wires can be monolithically constructed. Some        monolithic 3D and 3DIC approaches are described in U.S. Pat.        Nos. 8,273,610, 8,298,875, 8,362,482, 8,378,715, 8,379,458,        8,450,804, 8,557,632, 8,574,929, 8,581,349, 8,642,416,        8,669,778, 8,674,470, 8,687,399, 8,742,476, 8,803,206,        8,836,073, 8,902,663, 8,994,404, 9,023,688, 9,029,173,        9,030,858, 9,117,749, 9,142,553, 9,219,005, 9,385,058,        9,406,670, 9,460,978, 9,509,313, 9,640,531, 9,691,760,        9,711,407, 9,721,927, 9,799,761, 9,871,034, 9,953,870,        9,953,994, 10,014,292, 10,014,318, 10,515,981, 10,892,016; and        pending U.S. Patent Application Publications and applications,        Ser. Nos. 14/642,724, 15/150,395, 15/173,686, 16/337,665,        16/558,304, 16/649,660, 16/836,659, 17/151,867, 62/651,722;        62/681,249, 62/713,345, 62/770,751, 62/952,222, 62/824,288,        63/075,067, 63/091,307, 63/115,000, 2020/0013791, 16/558,304;        and PCT Applications (and Publications): PCT/US2010/052093,        PCT/US2011/042071 (WO2012/015550), PCT/US2016/52726        (WO2017053329), PCT/US2017/052359 (WO2018/071143),        PCT/US2018/016759 (WO2018144957), and PCT/US2018/52332 (WO        2019/060798). The entire contents of the foregoing patents,        publications, and applications are incorporated herein by        reference.    -   Electro-Optics: There is also work done for integrated        monolithic 3D including layers of different crystals, such as        U.S. Pat. Nos. 8,283,215, 8,163,581, 8,753,913, 8,823,122,        9,197,804, 9,419,031, 9,941,319, 10,679,977, and 10,943,934. The        entire contents of the foregoing patents, publications, and        applications are incorporated herein by reference.

Additionally the 3D technology according to some embodiments of theinvention may enable some very innovative IC devices alternatives withreduced development costs, novel and simpler process flows, increasedyield, and other illustrative benefits.

SUMMARY

The invention relates to multilayer or Three Dimensional IntegratedCircuit (3D IC) devices and fabrication methods. Important aspects of 3DIC are technologies that allow layer transfer. These technologiesinclude technologies that support reuse of the donor wafer, andtechnologies that support fabrication of active devices on thetransferred layer to be transferred with it.

In one aspect, a method to construct a 3D system, the method including:providing a base wafer; transferring a first memory wafer on top of thebase wafer; thinning the first memory wafer, thus forming a thin firstmemory wafer; transferring a second memory wafer on top of the thinfirst memory wafer; thinning the second memory wafer, thus forming athin second memory wafer; and transferring a memory control wafer on topof the thin second memory wafer; where the transferring a memory controlwafer includes bonding of the memory control wafer to the thin secondmemory wafer, and where the bonding includes oxide to oxide andconductor to conductor bonding.

In another aspect, a method to construct a 3D system, the methodincluding: providing a base wafer; processing a memory control circuiton top of the base wafer; transferring a first memory wafer on top ofthe memory control circuit; thinning the first memory wafer, thusforming a thin first memory wafer; transferring a second memory wafer ontop of the thin first memory wafer; and thinning the second memorywafer, thus forming a thin second memory wafer; where the transferringthe second memory wafer includes bonding of the second memory wafer tothe thin first memory wafer, and where the bonding includes oxide tooxide and conductor to conductor bonding.

In another aspect, a 3D device, the device including: providing a basewafer; processing a memory control circuit on top of the base wafer;transferring a first memory level on top of the memory control circuit;thinning the first memory level, thus forming a thin first memory level;transferring a second memory level on top of the thin first memorylevel; thinning the second memory level, thus forming a thin secondmemory level; where the transferring the second memory level includesbonding of the second memory level to the thin first memory level, andwhere the bonding includes oxide to oxide and conductor to conductorbonding.

In another aspect, a 3D device, the device including: a first stratumincluding first bit-cell memory arrays; a second stratum includingsecond bit-cell memory arrays; and a third stratum, where the secondstratum overlays the first stratum, where the first stratum overlays thethird stratum, where the third stratum includes a plurality of word-linedecoders to control the first bit-cell memory arrays and the secondbit-cell memory arrays; further including: a logic stratum; and athermal isolation layer disposed between the logic stratum and the firststratum, where the thermal isolation layer is designed so during thedevice operation a first temperature of the first stratum is at least20° C. lower than a second temperature of the logic stratum.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will be understood and appreciatedmore fully from the following detailed description, taken in conjunctionwith the drawings in which:

FIG. 1A is an example illustration of selective etch by Applied Materialetcher;

FIG. 1B is an example illustration of alternating Si and SiGe layers;

FIGS. 2A-2I are example illustrations of an alternative system processflow;

FIGS. 3A-3D are example illustrations of the structure transfer of analternative system process flow;

FIGS. 4A-4H are example illustrations of an alternative donor waferprocess flow;

FIGS. 5A-5D are example illustrations of an additional alternative donorwafer process flow;

FIGS. 6A-6D are example illustrations of structures and methods tothermally isolate stratums in a 3D IC;

FIG. 7 is an example illustration of a logic unit redundancy scheme;

FIG. 8 is an example illustration of an alternative logic redundancyscheme;

FIGS. 9A-9B are example illustrations of a staircase contact scheme;

FIGS. 10A-10J are example illustrations the formation and structure of astaircase connectivity scheme;

FIGS. 10K-10N are example illustrations of process simulations of theformation and structure of a staircase connectivity scheme;

FIGS. 11A-11D are example illustrations of a “Lego” scheme with 3DNOR;

FIG. 11E is an example illustration of an isolation structure to keepthe logic heat away from the memory array;

FIGS. 11F-11K are example illustrations of alignment techniques andstructures;

FIGS. 12A-12J are example illustrations of array access and staircaseschemes;

FIGS. 13A-13D are example illustrations of write and erase schemes forthe 3D NOR array;

FIG. 14A is an example illustration of I(V) curves of a silicidednanowire formed with microwave annealing technology;

FIG. 14B is an illustration of I(V) curves demonstrating the performanceof a self-referenced differential sense amplifier when applied to aprogrammed and erased memory cell;

FIGS. 15A-15E are example illustrations of a ‘DS-SB’ 3D NOR structureand cell formation;

FIG. 15F is an example illustration of a programming scheme for 3D NORwith a staircase;

FIG. 15G is an example illustration of an alternative to a staircase;

FIGS. 16A-16D are example illustrations of writing a ferroelectricmemory cell;

FIGS. 17A-17D are example illustrations of two bits stored in one facetof a memory cell;

FIGS. 18A-18D are example illustrations of writing bits in a smallsection of a ridge of the 3D-NOR fabric;

FIGS. 18E-18F are example illustrations of programming multiple bits ina cell of the 3S-NOR fabric;

FIG. 19A is an example illustration of a 3D system;

FIG. 19B is an example illustration of customization of a 3D system;

FIGS. 20A-20F are example illustrations of the formation of multiplestratum integrated into a 3D system via 3D integration with minimum perstrata processing;

FIG. 20G is an example illustration of a connectivity technique adaptedto die level operation;

FIG. 20H is an example illustration of a through strata via structure;

FIGS. 21A-21H are example illustrations of a control line arrangementfor memory integration of the 3D system of FIGS. 19 and 20;

FIGS. 22A-22B are example illustrations of a stratum select connectivityscheme;

FIGS. 22C-22E are example illustrations of wordline and bitline selectschemes;

FIG. 22F is a section of a partition an array of memory units;

FIGS. 23A-23B are example illustrations of two-layer select and selectschemes;

FIG. 24A is an example illustration of an alternative 3D computersystem;

FIG. 24B is an example illustration of a generic 3D memory structure“G3DM”;

FIG. 24C is an example illustration of 3D structure with active thermalcooling;

FIGS. 25A-25D are an example illustrations of an alternative flow andstructure for 3D stacking without changing the main processing of thememory/logic;

FIG. 25E is an example illustration of forming alignment marks for themethod and structure of FIGS. 25A-25D;

FIGS. 25F and 25G are example illustrations of using a lithographicallydefined doping process to simplify 3D stacking;

FIGS. 25H-25J are example illustrations of over the array connectivitystructures;

FIGS. 26A-26D are example illustrations of using a punch and plugprocess scheme;

FIG. 26E is an example illustration of the single hole punch process toconstruct elements which may be needed for the 3D NOR fabric;

FIG. 26F is an example illustration of holes/vias etched or punchedtogether/simultaneously;

FIG. 26G is an example illustration of holes/vias etched or punched intwo or more independent etch steps;

FIG. 26H is an example illustration of global strata select for stackingof 3D memory structures;

FIG. 27 is an example illustration of a memory unit refresh operationflow;

FIG. 28 is an example illustration of an alternative per layer access bysidewall strapping though one-time-programmable anti-fuses; and

FIGS. 29A and 29B are example illustrations of a pass-through pathadd-on structure and an alternative structure.

DETAILED DESCRIPTION

An embodiment of the invention is now described with reference to thedrawing figures. Persons of ordinary skill in the art will appreciatethat the description and figures illustrate rather than limit theinvention and that in general the figures are not drawn to scale forclarity of presentation. Such skilled persons will also realize thatmany more embodiments are possible by applying the inventive principlescontained herein and that such embodiments fall within the scope of theinvention which is not to be limited except by any appended claims.

Some drawing figures may describe process flows for building devices.The process flows, which may be a sequence of steps for building adevice, may have many structures, numerals and labels that may be commonbetween two or more adjacent steps. In such cases, some labels, numeralsand structures used for a certain step's figure may have been describedin the previous steps' figures.

The use of layer transfer in the construction of a 3D IC based systemcould enable heterogeneous integration where each of strata may includeone or more of MEMS sensor, image sensor, CMOS SoC, volatile memory suchas DRAM and SRAM, persistent memory, and non-volatile memory such asflash and OTP. Such could include adding memory control circuits, alsoknown as peripheral circuits, on top or below a memory array. The memorystrata may contain only memory cells but not control logic, thus thecontrol logic may be included on a separate strata. Alternatively, thememory strata may contain memory cells and simple control logic wherethe control logic on that strata may include at least one of decoder,buffer memory, sense amplifier. The circuits may include the chargepumps and high voltage transistors, which could be made on a stratausing silicon transistors or other transistor types (such as SiGe, Ge,CNT, etc.) using a manufacturing process line that is different than thelow voltage control circuit manufacturing process line. The analogcircuits, such as for the sense amplifiers, and other sensitive linearcircuits could also be processed independently and be transferred overto the 3D fabric. Such 3D construction could include “Smart Alignment”techniques presented in this invention or leverage the repeating natureof the memory array to reduce the impact of the wafer bondermisalignments on the effectiveness of the integration.

In patents such as, for example, U.S. patent application Ser. No.15/173,395, layer transfer techniques called ELTRAN (epitaxial layertransfer) are presented and may be part of the formation process of a3DIC. The ELTRAN technique utilizes an epitaxial process or processesover porous layers. Alternatively other epitaxial based structures couldbe formed to support layer transfer techniques by leveraging the etchselectivity of these epitaxial layers, such as the very high etchselectivity of SiGe vs. Silicon, and variations such as Silicon (singlecrystal or poly or amorphous), SiGe (mix of silicon and Germanium), Pdoped silicon, N doped silicon, etc. Alternately, these layer(s) couldbe combined with types of detachment processes, such as ‘coldsplitting,’ for example the Siltectra stress polymer and low temperatureshock treatment, to provide a thin layer transfer process.

Recently it become a very attractive concept for processing gate allaround horizontal transistors and has become the target flow for nextgeneration devices such as the 5 nm technology node. Some of the work inrespect to selective etching of SiGe vs. silicon has been presented in apaper by Jang-Gn Yun et al. titled: “Single-Crystalline Si Stacked Array(STAR) NAND Flash Memory” published in IEEE TRANSACTIONS ON ELECTRONDEVICES, VOL. 58, NO. 4, APRIL 2011, and a more recent work by K. Wostynet al. titled “Selective Etch of Si and SiGe for Gate All-Around DeviceArchitecture” published in ECS Transactions, 69 (8) 147-152 (2015), andby V. Destefanis et al. titled: “HCl Selective Etching of Si1-xGexversus Si for Silicon On Nothing and Multi Gate Devices” published inECS Transactions, 16 (10) 427-438 (2008), all of the forgoingincorporated herein by reference. Since the SiGe over Si substrateprocess is becoming mature, this facilitates using a SiGe layer as asacrificial layer for production worthy 3D layer transfer. FIG. 1Aillustrates the high etch selectivity of SiGe vs. Silicon, which, inthis example, could be formed using, for example, the Applied MaterialSelectra etch system. Alternatively, the selective etch may be madeusing a wet chemical etch. FIG. 1B illustrates a putative retrograde Gecomposition with stack thickness as explained thoroughly later.

An exemplary layer transfer process could include the steps A-K,referencing the illustrations FIG. 2A-2I and FIG. 3A-3D:

A. As illustrated in FIGS. 2A and 2B, epi (the term ‘epi’ herein meansepitaxial, as often used in the art) layer 204 such as SiGe may beformed on a donor wafer or reusable donor wafer-base substrate 202, forexample, by an epitaxy processes. The donor wafer may contain a stratalayer over the sacrificial layer, also called herein a ‘cut-layer’, onthe base substrate 202 where the strata layer is subsequentlytransferred to a receptor wafer. The epitaxy process may utilize but notis limited to vapor-phase epitaxy (WE), a modification of chemical vapordeposition, molecular-beam and liquid-phase epitaxy (MBE and LPE). Ifdesired so as to at least increase etch selectivity, dopant may beincorporated during the epitaxial growth process by adding impurities tothe source gas and/or reaction chamber. The type of epitaxy may behomoepitaxy with the same material grown on the base substrate 202. Inthe homoepitaxy, the doping type and concentration of the epi layer 204may be substantially different from those of the base substrate 202 andthe subsequently formed silicon layer 206, which could providesufficient etch selectivity. Alternatively, another type of epitaxy maybe heteroepitaxy with different material grown on the substrate. Suchexamples include SiGe on Si. Epi layer 204 may be formed with athickness of about 20 nm, 50 nm, 100 nm, or about 200 nm, or about 500nm, or about 1000 nm or about 2000 nm, depending on process integration,etching throughput, stiction resistance, and other process and devicearchitecture engineering decisions and tradeoffs. The base wafer 202thickness could be similar to the industry standard for these types ofprocessing such as about 775 microns used for most current silicon fabs.The base wafer 202 may include sizes of about 2 inch, about 4 inch,about 8 inch, or about 12 inch in diameter or about 16 inch in thefuture (these wafer diameter sizes are often known with thecorresponding mm sizes: 50 mm, 100 mm, 150 mm, 200 mm, 300 mm, 450 mm).Heterogeneously grown epi layer 204 may include various materials, forexample SiGe, in anticipation of a sacrificial etch later in the processflow. The content of Ge in the SiGe may be designed per the selectivitydesired and in consideration of the stress, for example, such as about20% Ge, or about 10% Ge, or about 25% Ge, etc. With respect to the etchselectivity, the epi layer 204 could be favorably removed from the basesubstrate 202 and the subsequently formed silicon layer 206. The levelof stress needs to be controlled to not cause dislocations. The stresscan be controlled by at least growth rate, temperature, and filmthickness. Predefined trenches on the silicon layer 206 and partially orfully across the epi layer 204 (not shown) in the designated dicingstreets (or other non-circuit areas, for example, such as the streetsbetween projection fields) could be used to provide some release of thepotential stress. These trenches could have a width and a depthapproximately corresponding to the thickness of the SiGe layer. Othertechniques could be used to reduce stress, associated with epitaxial ofSiGe on or under a silicon layer, such as incorporating smaller atoms inthe SiGe layer such as boron or carbon; these and similar techniques areknown in the art and could be used with combination with the techniquesherein to support various forms of layer transfer or other applicationsherein.

B. As illustrated in FIG. 2C, silicon layer 206 as an active layer forthe active devices to be formed may be epitaxially grown on top of epilayer 204. The silicon layer 206 may also be single crystalline Ge, SiGeor Si:C depending on the applications. However, we herein will usesilicon layer 206 as the active layer unless otherwise specified. Thethickness of silicon layer 206 may include a thickness of about 10 nm,or about 20 nm, or about 50 nm, or about 100 nm, or about 200 nm, orabout 500 nm, or about 1,000 nm or about 2,000 nm, as desired for theelectronic circuits, depending on engineering, materials and scientificdevice considerations. In many formations, silicon layer 206 may beconsidered to consist of mono-crystalline or single crystal silicon.

C. As illustrated in FIG. 2D, desired circuits 212 may be processed,including n-type and p-type transistors and other devices, such asinductors, capacitors, resistors, optoelectronic devices, gas sensors,etc., and may include a processed contact layer. For example, thedesired circuit 212 may be processed to include metal 0 layer or metal 4layer. This could be done using conventional processing including theappropriate high temperature processes (˜600-900° C.) such as gateoxidation, dopant activation, contact silicidation, and so on. Types oftransistors and circuits may include, for example, DRAM, NAND, or RRAM,RCAT, continuous array and FPGA structures, gate array, memory blocks,logic blocks, CMOS p-type and n-type transistors, MOSFET transistors,junction-less transistors, JFET, replacement gate transistors,thin-side-up transistors, double gate transistors, horizontally orientedtransistors, finfet transistors, fully depleted thin-body transistor,JLRCAT, DSS Schottky transistors, and/or trench MOSFET transistors.

D. As illustrated in FIG. 2E, first set of holes 214 may be formed (by,for example, a conventional mask and etch sequence of processing) andmay extend through the top silicon layer 206. The bottom of the etchedtrench may reside inside the SiGe epi layer 204 and may not touch thesurface of base substrate 202 in order to reclaim the base substrate202. Alternatively, the bottom of the etched trench may be located belowthe bottom of SiGe epi layer 214. These holes could then be filled withoxide or other material that would remain and play as a supporter forthe desired circuits during future silicon and SiGe etches. Filled firstset of holes 214 may serve as posts to hold the top layer designated tobe transferred in later steps. First set of holes 214 may be located inthe dicing streets area or some field oxides such as shallow trenchisolation, and may be designed to be weak enough to be torn out,according to design and process integration engineering considerations.

E. As illustrated in FIG. 2F, one or more interconnection layers 216 maybe added. This is optional, depending on engineering and designconsiderations. Interconnection layers 216 may include wiring, contactsand vias, and may include materials such as, for example, copper,aluminum, tungsten, titanium, tantalum, cobalt metals and/or silicidesof the metals. Interconnection layers 216 may be covered with isolationlayer 222 (as illustrated in FIG. 2G) with materials such as SiO₂,carbon containing oxides, and so on. Isolation layer 222 may beplanarized, for example, with CMP or other forms of planarization inanticipation of future wafer to wafer bonding.

F. As illustrated in FIG. 2H, second set holes 224 may be formed toexpose portions of sacrificial SiGe epi layer 204, thus allowing asubstantially full etch of the sacrificial SiGe layer (the former SiGeepi layer 204). These holes could be made at un-used locations or inlocations designated for future Through-Layer-Via (TLVs). These holescould also be made in locations designated for shallow trench isolation(“STI”). These holes may be opened through the top layers such asisolation layer 222 all the way into the epi layer 204. The formation ofthe holes for the sacrificial layer etches may include steps to protectthe top silicon layer 206 and its holes side wall such as sidewallspacer by: 1. Use isotropic deposition techniques such as ALD to depositisolation material such as silicon oxide in the open holes covering theside wall and the bottom of the holes. 2. Then may use anisotropicetching to open only the bottom of the holes to direct access to thesacrificial layers while protecting the side walls.

G. As illustrated in FIG. 2I, selectively etch the remaining sacrificialepi layer 204 creating void 226 underneath desired circuit layer 212.The design of posts and allocation of sacrificial etch holes could bedesigned so after the sacrificial layer etching is completed, thesuspended circuit layer be remained substantially flat for layertransfer.

H. As illustrated in FIG. 3C, the structure such as illustrated in FIG.3A (the structure from FIG. 2I) may be flipped and bonded onto a targetwafer 302 illustrated in FIG. 3B. The target wafer 302 may be fullyprocessed wafer including metallization, for example, an arbitrarilydesigned SoC or generic circuit. Alternatively, the target wafer 302 maybe specially fabricated wafer which could be the underlying base in the3D structure. For example, see the incorporated references listed aspart of the Background of the Invention section of this specification.This results in bonded structure 390 such as illustrated in FIG. 3C. Thebonding could be oxide to oxide bonding which could be followed with topwafer interconnection through a TLV (Thru Layer Via) process, or metalto metal bonding, or hybrid bonding (oxide to oxide and metal to metalbonding). The bonding process could be made so it results insufficiently a strong adhesion between bonding surfaces of donor waferand the target wafer 302. The target wafer 302 may include transistorsof one or more types in one or more layers, metallization such as, forexample, copper or aluminum in one or more layers, interconnections toand between layers above and below, and interconnections within thelayer. The transistors may be of various types that may be differentfrom layer to layer or within the same layer. The transistors may be invarious organized patterns. The transistors may be in various patternrepeats or bands. The transistors may be in multiple layers involved inthe transfer layer. The transistors may be, for example, junction-lesstransistors or recessed channel array transistors. Target wafer 302 mayfurther comprise semiconductor devices such as resistors and capacitorsand inductors, one or more programmable interconnects, memory structuresand devices, sensors, radio frequency devices, or optical interconnectwith associated transceivers. Target wafer 302 may further includeisolation layers, such as, for example, silicon and/or carbon containingoxides and/or low-k dielectrics and/or polymers, which may facilitateoxide to oxide wafer or substrate bonding. Target wafer 302 may also bea base substrate to build the 3DIC stricture onto.

I. The donor structure, substantially donor wafer-base substrate 202,may be detached from bonded structure 390 leaving intermediate 3D ICstructure 399 as is illustrated in FIG. 3D. The donor wafer,substantially reusable donor wafer-base substrate 202, could bereclaimed for processing to prepare for reuse, perhaps as a seed waferof subsequent epitaxial growth as explained in FIG. 2. Intermediate 3DIC structure 399 may include target wafer 302, desired circuits 212,surface 213, first set of holes 214, and interconnection layers 216.Alternatively, the substrate 202 could be grind and etched back withoutbeing reusable for future processing.

J. The top surface 213 of intermediate 3D IC structure 399 may becleaned and prepared for interconnections. Optionally cover withisolation.

K. TLVs may be formed for interconnection from the top to the bottomstrata to form the 3DIC layer interconnects if necessary.

The donor wafer ‘tearing off’ detach could be assisted by knowntechniques such as, for example, water-jet, wedge, laser cutting, etchedassisted tearing off and mechanical twist and pull.

Alternatively, additional interconnection layers and other processingcould be added in between step ‘G’ and ‘H’ above. So, the structureillustrated in FIG. 2I could be further processed before being flippedand bonded to the target wafer 302. This add-on process could includeadding additional metal layers or any other structure includingadditional transistor layers using similar techniques such as layertransfer.

The sacrificial layer removal holes 224 process could include side walloxide deposition to further protect the side walls from the etch processdesigned to remove the sacrificial layers. These holes could be latersealed by a second step of, for example, oxide deposition. Such twosteps oxide fill could be visible under proper magnification or otherimaging techniques.

These layer transfer techniques could allow many of the benefitsassociated with monolithic 3D technologies including avoiding thermalbudgets associated with forming one circuit strata affecting anothercircuit stratum, enabling mixing of technology nodes, mixing circuitsubstrate types, crystal structure, orientation and many otheradvantages associated with heterogeneous integration without processtemperature restrictions described herein and in the incorporated art.

The use of SiGe for epitaxial based ‘cut layer’ instead of poroussilicon or porous SiGe ‘cut layer’ could be adapted to many of the flowspresented in at least U.S. application Ser. Nos. 14/642,724, 15/095,187,and 15/173,686, all the forgoing are incorporated herein by reference.It does add some complexity related to the holding posts formation andthe holes to etch the SiGe thoroughly prior to performing the layertransfer. For applications in which two layers of active silicon, andisolation layer in between, is desired, the in-between SiGe could beremoved after the transfer and replaced with isolation material.

Use of SiGe as a sacrificial layer for transferring a single crystalstructure of one crystal on top of another structure has been presentedin U.S. patent application 2015/0137187, incorporated herein byreference. Many studies of SiGe etch selectivity in respect to siliconhave been done and published such as: In a work by T. Salvetat et altitled “Comparison between three Si1-xGex versus Si selective etchingprocesses” presented at 214th ECS Meeting; and by M. Stoffel titled“SiGe wet chemical etchants with high compositional selectivity and lowstrain sensitivity” published in Semicond. Sci. Technol. 23 (2008)085021; by V. Destefanis et al titled “High pressure in situ HCl etchingof Si1-xGex versus Si for advanced devices” published in Semicond. Sci.Technol. 23 (2008) 105019; by T. K. Cams et al titled “Chemical Etchingof Si,Ge in HF:H202:CH3COOH” published in J. Electrochem. Soc., Vol.142, No. 4, April 1995; and by Marius Orlowski et al titled “Si, SiGe,Ge, and III-V Semiconductor Nanomembranes and Nanowires Enabled by SiGeEpitaxy” published at ECS Transactions, 33 (6) 777-789 (2010), all ofthe forgoing are incorporated herein by reference.

Another alternative is to skip steps related to FIG. 2D-2I and use theSiGe layer 204 as an etch stop, and after transfer grind and etch backthe donor substrate 202, using the SiGe as an etch stop. And if desired,remove the SiGe layer 204 with an additional selective etch step,etching SiGe and very little or negligibly thin backside of the topsilicon 206. The base substrate 202 could be about 775 microns thickwhile the SiGe 204 could be ten nm or less, or few tens of nm or evenfew 100 nm. For example, a 3D technique of flip bond and etch back of anSOI donor such as presented in at least U.S. Pat. Nos. 6,821,826,7,723,207 and 7,312,487, all the forgoing are incorporated herein byreference. As an alternative to the use of SOI wafers, the basesubstrate 202 would not be reused but rather be ground and etched awayfrom its wafer backside. The back grind and etch back could use wetetching and the SiGe layer 204 could be designed to be very resistive tothe silicon wet etching. The SiGe could be designed to have multiplelayers including one that might have high Ge content, for example, suchas over about 20% or over about 40% or over about 80%, followed by otherlayers with low Ge content such as less than about 20% or even less thanabout 10% to reduce stress so to support the silicon layer 206. FIG. 1Billustrates an example of having the alternating Si and SiGe layersbeing comprised by multiple sub-layers with a varying content of Ge inthe SiGe. Depositing or epitaxially growing the SiGe interface layer tothe silicon with a smaller amount of Ge content decreases the stress dueto the lattice mismatch. Then gradually increasing the Ge content to thedesired level and then after the desired thickness has been growngradually reducing the Ge content toward the next level of silicon couldbe used to reduce stress from both sides of the Silicon-SiGe-Siliconstructure. Reducing the stress could help reduce the risk for formationof point defects and dislocations, and could help the engineering of theSiGe thickness as needed for the application. The alternative of use ofSiGe as an etch stop later is further discussed herein later.

Alternatively, the ‘cut’ process could be integrated with Siltectra's‘Cold Split’ technology as has been detailed in at least U.S. Pat. Nos.8,440,129 and 8,877,077, and U.S. applications 20160064283, 20160086839,all of which are incorporated herein by reference. These techniqueswould allow reuse/recycling of the donor wafer (base substrate 202Amiddle location inside SiGe or the interface between Si and SiGe couldbe used to provide the “Pre-Defined Break Initiation Point” as analternative to the Siltectra use of laser or in addition to it. TheSiltectra's ‘Cold Split’ could reduce the need for the undercut etch andposts formation processing while providing reuse of the base substrate202. For this technique, a multilevel SiGe could be designed to supportthe ‘cut’ on the one hand but also to reduce damage to the device layeron the other. This could be accomplished by increasing the Ge content inthe interface with the base substrate 202 to have high Ge content suchas over about 20% or over about 40% or even over about 80% and then onthe side interfacing with device layer 206 forming a low Ge content suchas less than about 20% or even less than about 10% to reduce stress tothe silicon circuit layer 206. Alternatively, a few atomic layers thickGe rich SiGe layer or even a pure Ge layer maybe used as a predefinedbreak layer.

Once the base substrate 202 is removed, a selective etch could be usedto remove the SiGe residues. Additional thinning processes such as etchand/or CMP could be used to further thin the back side of the devicelayer 206. Connection layers could be added included vias aligned to thetarget wafer 302 using “Smart Alignment” and similar 3D integrationtechniques discussed here and the incorporated by reference art.

This use of Cold Split could be used to form SOI wafers and could beless expensive to manufacture when compared to the current ion-cutmethods.

A variation of flow in respect to FIG. 2A-2I, is to have the first setof holes 214 posts formed as part of the substrate process prior todesired circuits 212 processing. Accordingly, the flow in respect toFIG. 2E could be done to the donor wafer illustrated in FIG. 2C. Theseposts could be positioned at the dicing streets such as those betweenreticle projections, so they would not interfere with the future desiredcircuits 212. Alternatively post formation may be done to the donorwafer illustrated in FIG. 2B, which could then be processed with anepitaxial process which could be thick enough to fill-in the space ontop of these posts allowing the following circuit processing withoutconcern for the posts' locations. The number of posts per wafer could be1-2, 4-10, 10-50 or over 100 first set of holes 214 posts per reticle.The diameter of these posts could be the size of vias for the designatedprocess, or 50-100, 100-200, 200-400 nm or even larger. The material inthese posts could be material compatible with these semiconductorprocesses and may be designed to be very selective with respect to theSiGe etch such as Silicon-Nitride, or any of the materials used forcontacts such tungsten, or their combination, or, for example, copper,aluminum, titanium, tantalum, cobalt metals and/or silicide of themetals.

Another alternative is to use a similar flow to form a donor substratewhich could support layer transfer as an alternative to an ELTRAN baseddonor wafer. This embodiment offers silicon on nothing structuresanchored by post structures on the silicon ends. Then, the processfollows using wafers with silicon on nothing. An exemplary donor waferconstruction flow could include the steps A-F, referencing theillustrations in FIG. 4A-4H:

A. As illustrated in FIGS. 4A and 4B, on a reusable donor wafer-basesubstrate 402 and epi layer 404 as a sacrificial layer may be formed,for example, by epitaxy processes. Epi layer 404 may be formed with athickness of about 100 nm, or about 200 nm, or about 500 nm, or about1000 nm or about 2000 nm, depending on process integration andarchitecture engineering decisions and tradeoffs. Epi layer 404 mayinclude various materials, for example SiGe, in anticipation of asacrificial etch later in the process flow. The content of Ge in theSiGe may be designed per the selectivity desired and in consideration ofthe stress. Predefined trenches (not shown) in the designated dicingstreets (or other non-circuit areas, for example, such as the streetsbetween projection fields) could be used to release the potentialstress. These trenches could have a width and a depth approximatelycorresponding to the thickness of the epi layer 404 SiGe layer.

B. As illustrated in FIG. 4C, first epi silicon layer 406 as an activedevice layer may be epitaxially grown on top of epi layer 404. Thethickness of silicon layer 406 may include a thickness of about 10 nm,or about 20 nm, or about 50 nm, or about 100 nm, or about 200 nm, orabout 500 nm, or about 1000 nm or about 2000 nm, as desired for theelectronic circuits, depending on engineering, materials and scientificdevice considerations. In many formations, first epi silicon layer 406may be considered to consist of mono-crystalline or single crystalsilicon.

C. As illustrated in FIG. 4D, first set of holes 414 may be formed toeventually be anchors of silicon on nothing structures (by, for example,a conventional mask and etch sequence of processing) and may extendthrough the first epi silicon layer 406 and the SiGe epi layer 404.These holes could then be filled with silicon nitride or oxide or othermaterial that would be remained to future silicon and SiGe selectiveetches. Filled first set of holes 414 may serve as posts to hold the toplayer designated to be transferred in later steps. First set of holes414 may be located in the dicing streets area and may be designed to beweak enough to be torn out at the ‘cut’ step, by methods, for example,such as mechanical tear-off, edge and twist tear-off, water jet,according to design and process integration engineering considerations.

D. As illustrated in FIG. 4E, form multiple second holes 424 to exposethe SiGe layer 404 and resultantly allow a full etch of the sacrificialSiGe layer (the former SiGe epi layer 404). These holes need to be openthrough the first epi silicon layer 406 all the way into the SiGe epilayer 404.

E. As illustrated in FIG. 4F, selectively etch the sacrificial SiGelayer creating void 426 underneath the first epi silicon layer 406. Thesuspended first epi silicon layer 407 may remain substantially flat forgood bonding process.

F. As is illustrated in FIG. 4G perform additional epitaxial processingadding second epi silicon 432 (incorporated suspended first epi siliconlayer 407 in drawing) and sealing second holes 424. The material anddoping type of second epi silicon 432 may be the same or different fromthose of the first epi silicon 406 depending on the applications. Theadditional epitaxial width could exceed the second holes 424 radius toease the holes sealing. A smoothing technique such as chemicalmechanical polishing and H₂ annealing could be used to improve the toplayer surface.

The donor wafer illustrated in FIG. 4G could then be used to processcircuits 212, similar manner such as illustrated in FIG. 2D and couldform some interconnections 216 similar manner as illustrated in FIG. 2F,and then be flipped and bond on top of a target wafer in a similar flowas is illustrated in FIG. 3A-3D, and many flows presented in theincorporated by reference material, such as U.S. Ser. No. 15/173,686 inrespect to ELTRAN base donor wafer.

The silicon epitaxial layer 206/406 could be constructed from two layerssuch as first layer doped n+ followed by p− doped layer. Such doublelayer construction could allow smoothing of the surface 213 of thetransferred layer after the transfer. Selective etch could etch thedoped n+ layer leaving a smooth p− doped layer. Alternatively, thesilicon epitaxial layer 206/406 could be made with three layers as isillustrated for example in FIG. 4H. First a p− layer 442, followed by n+layer 444 and finally the upper most p− layer 446. The upper layer 446could be used for the transistor layer, underneath it layer 444 whichcould support back-bias as suggested by Zeno Semiconductors and aspublished such as in papers by Jin-Woo Han et al titled “A NovelBi-stable 1-Transistor SRAM for High Density Embedded Applications”published at IEDM 2015, and “A CMOS-Compatible Boosted TransistorHaving >2× Drive Current and Low Leakage Current” published at ESSDERC2016, incorporated herein by reference. And the bottom layer 442, as asacrificial layer, to support smoothing, post transfers by selectiveetch as discussed above.

In U.S. patent application Ser. Nos. 15/095,187 and 15/173,686incorporated herein by reference, ELTRAN base layer transfer techniquesare shown being adapted to support die to wafer 3D IC construction. Someof the die-to-wafer flows suggest transfer of dies having a relativelygreater thickness such as 6 microns or even 20 microns and furtherthinning these dies after being bonded to the target wafer. Such diethinning could leverage a multi layers die structure. As an example, amultilayer such as is illustrated in FIG. 4H could be used. For such thebottom layer 442 could be silicon on top of it SiGe layer 444 and at thetop silicon device layer 446. So the multilayered 440 could be ‘cut’ andbonded at a die level onto the target wafer, then a selective etch fromthe top could be used to first remove the silicon layer 442 and thenthin the die all the way to the device layer by selectively etching theSiGe layer 444. These extra layers 442 and 444 could have a thickness ofabout 1 micron, 1-3 microns, 3-6 microns or even higher. The devicelayer 446 itself could have more sub-layers such as n+ and p− to supportthe back-bias scheme as discussed before. The use of multilayers, suchas SiGe, allows having flexibility so a layer thickness is first set tosupport transfer at the wafer or die level providing the mechanicalstrength required for the handling and transfer, to be followed byselective etch trimming the thickness of the devices to support theelectrical function and to allow forming via and other connection forfollowing steps. These could be engineered by the artisan in the art.The ‘cut’ techniques could include selective under-etch or grinding andetch back as could be engineered for specific applications.

All these multilayer structures could be formed during the epitaxialgrowth by adding materials as gases to the epitaxial growth chamber aswell known in the art.

These variations could be used for donor wafer substrate formation asdiscussed in reference to FIG. 4A-4H, or for transferable device layeras discussed in reference to FIG. 2A-2I.

As been stated before, a buried SiGe layer could be used as an etch stoplayer. Use of buried SiGe as an etch stop layer to transfer acrystalline layer on top of another wafer structure has been presentedin U.S. Pat. Nos. 6,521,041, 6,689,211, 6,940,089, 7,348,259 and U.S.patent applications 2014/0342523, and in combination with ion cut inU.S. patent applications 2007/0023066, 2008/018959 all of the forgoingare incorporated herein by reference.

An additional alternative is to combine the porous formation technologyof the ELTRAN based wafer transfer with the epitaxial ease of formationof silicon—SiGe technology base layer transfer presented herein. In U.S.Pat. Nos. 5,685,946 and 5,757,024 and in paper by Mondiali, V., et al.“Micro and nanofabrication of SiGe/Ge bridges and membranes bywet-anisotropic etching.” Microelectronic Engineering 141 (2015):256-260, all incorporated herein by reference, SiGe is shown to be stainetched forming a porous layer with about 100 to 1 selectivity withrespect to silicon. Using this selectivity could allow forming a‘cuttable substrate’ from the structure of FIG. 2C or FIG. 4C withoutthe need of the posts formation of FIG. 2E or FIG. 4D. This conceptcould be applied to substantially all of the transfer flows presentedherein including die level and wafer level transfer. The buried SiGelayer would become mostly porous Ge or porous SiGe layer and wouldwithstand the following process temperature and other related processsteps. For the ‘cut’ step the techniques presented in respect to theELTRAN process could be used, such as mechanical tear-off, edge andtwist tear-off, water jet, and extremely selective etch (being porousand Ge vs. silicon). This would simplify the layer transfer process andwould allow substrate reuse, both cost saving opportunities.

The stain etch of a buried (Si or Ge or) SiGe layer converting it toporous layer could also be used when thermal isolation is required.Porous layers function well as a thermal isolation layer and oxidizingit could further add mechanical strength and further decrease itsthermal mobility. Accordingly such a layer process could be useful informing thermal isolation between the stratum of the 3D structure. So,for example, using SiGe as an etch stop could be followed by, instead ofetching away the SiGe after grinding and etching of the siliconsubstrate, stain etching the SiGe converting it to a thermal isolationlayer.

Converting the buried SiGe layer to porous layer by stain etching aspresented above could leverage the STI etching step to use it as accessto the buried SiGe layer or could include dedicated holes 224, 424,etching step. These access holes could be designed to provide access foreffective conversion of the full buried SiGe layer underneath the die toSiGe. Such full buried SiGe conversion could be engineered based on theheight of the buried SiGe layer the percent of Ge and other engineeringaspects. As presented in U.S. Pat. Nos. 5,685,946 and 5,757,024 the sidespread of the stain etching could extend to over 1 micron from theaccess holes. The engineering aspect of such full SiGe conversion couldinclude Electronic Design Automation (“EDA”) to support the designprocess to place these holes throughout the die surface to providesufficient access to full SiGe stain etching. Such EDA support couldinclude adapting the macro-cell library to include access for very largestructures, providing a holes adder utility to add holes in ‘white’spaces area that do not need holes or STI for the active circuits, andadding modules to the Design Rule Checker (“DRC”) utilities Similar typeof EDA enhancements to support process modules, is common practice inthe industry.

The layer transfer process could include two steps. First step could beperformed at the frontend of the line of the process optionally as partof the STI process in which the SiGe layer is stain-etched converting itto a substantially porous layer. The second step could be performed justas before the layer transfer. In this second step, the porous-SiGe layeris selectively etched to make it ready for “cut”—detach. At that pointthe porous-SiGe could be selectively etched with extremely highselectivity. As discussed before, etching porous layer is about 5 ordersof magnitude faster than etching the respective same material in fullsolid form. In addition the porous-SiGe is mostly Ge which could beextremely selective etched in respect to silicon. Accordingly theporous-SiGe could be etched with many orders of magnitude selectivityvs. silicon or other elements of the active circuits. In this case, thetop silicon sidewall protection process described in FIG. 2H and FIG. 2Imay be skipped. For the second step of weakening the porous-SiGe therequired deep holes access could be designed with very low area loss. Anexample for such low cost access could be using the dice lanes. Deepetch of the dice lanes could help the layer transfer and detachingprocess as ‘divide and conquer’. Additionally, the second step ofweakening the porous-SiGe etch could be design to leave only smallporous regions in the center of dies, keeping the dies in place for thebonding but make it easy to then detach the wafer leaving the active diebonded and the substrate detached and ready to be refreshed for reuse.An additional aspect of these porous-SiGe and related layer transfertechniques herein is an improved bonder machine which could include adetaching module. Such a detaching module could be a simple twist andpull apart, tearing off the substrate for reuse.

Additionally, a substrate 502 similar to one illustrated in FIG. 2Ccould be used in a conventional semiconductor fabrication process toprocess device layer contacts and potentially some connectivity 516 asillustrated in FIG. 5A. The SiGe layer 518 could be made as a bufferlayer with multiple gradient Ge or as a uniform SiGe with Ge content of15-20% or 20-30% or even higher. The circuit layer could be covered withoxide layer 517 and then planarized and made ready for being bonded to atarget wafer 504 shown in FIG. 5B. The target wafer 504 may also beprocessed with the desired level of metallization. An oxide to oxidebond could be used to bond it to the target wafer 504 as illustrated inFIG. 5C. Other types of bonding could be used; such as metal to metal orhybrid bonding. Then a grind and etch could be used to remove thesilicon substrate 502 from the bonded structure 522 leveraging the SiGelayer 528 as an etch stop resulting with the structure 524 as isillustrated in FIG. 5D.

Alternatively, the substrate 502 could be made with perforations similarto as been described in U.S. Pat. No. 8,273,610, incorporated herein byreference, in respect to at least FIG. 184 and FIG. 185. The SiGe layercould be etched or stain etched through these perforations allowing thedetachment of the carrier wafer 502 for reuse.

Additional advantage of the techniques described herein is having thetransferred circuit being an SOI circuit with its active siliconthickness to be fully depleted channel. The single crystalline siliconlayer such as 530 could be made thin enough and being bonded over oxideand covered with oxide effectively could provide the SOI functionalityand if made thinner such as 10 nm provides FD SOI functionality.

FIG. 6A is a ‘cuttable’ wafer carrying circuits 610 such as memorycontrol (periphery) circuits. FIG. 6D illustrates transferring thecircuits 610 of FIG. 6A on top of the structure 604 of FIG. 6B,transferring the substrate 601 and partially the ‘cut-layer’ (SiGe) 603,and then removing base substrate 601 and partially the ‘cut-layer’ 603.An additional inventive embodiment is to optionally form a thermalisolation 608 on top of the memory matrix of target wafer 604 as isillustrated in FIG. 6B. In U.S. Pat. No. 9,023,688, incorporated hereinby reference, in at least FIGS. 1-5 and associated specificationsections, various thermal isolation layer techniques are presented toallow high temperature processing of the upper layer with minimal effectof the underlying circuit. These techniques could also be used to allowthermal isolation between one stratum and the other strata. Such couldhelp isolate the operating temperature of one stratum so that it wouldnot affect the operation of the other stratum. For example, the targetwafer 604 could be primarily memory circuits while the transfer circuit610 could be logic circuits that consume higher power during operation.The logic circuit might be generating heat and operate at a highertemperature that the memory circuit underneath; for example, atemperature difference of greater than about 20° C., greater than about40° C., greater than about 60° C., greater than about 100° C.Accordingly forming a thermal isolation layer 608 in-between might helpisolate temperature across these strata. Such isolation layer techniquescould also include having layer 608 act as a sacrificial layer thatcould be etched under the bonding layer 606 in similar way to what havebeen described in respect to the SiGe layer 204 in reference to FIG. 2Dto FIG. 2I. Etching away layer 608 results as is illustrated in FIG. 6C,could further increase the thermal isolation by providing an air gapisolation 630 between stratums. The etch technique could be such whichforms a first porous layer which could be fully oxidized providingburied air pockets and thus almost an air gap level of thermalisolation. Using these techniques could allow forming a thermalisolation layer 630 between two strata having a thickness of few tens ofnm or few hundreds of nm or even few microns, and having a low thermalconductivity such as less than about 1 W/mK or less than about 0.4 W/mKor less than about 0.1 W/mK or even less than about 0.05 W/mK.Alternatively, the isolation layer, for example, thermal isolation 608,630 in between the target wafer 604 circuits and the transfer circuits610 could comprise aerogel or high porosity dielectric as detailed inU.S. Pat. No. 9,023,688 and could be made extra thick to furtherincrease the thermal isolation, such as, for example, greater than about100 nm, greater than about 200 nm, greater than about 400 nm, or greaterthan about 1 micron thick. In some cases, a thickness of 1-10 micronsmay be indicated, depending on design and engineering tradeoffs.Additionally, bonding layer 606 could include a heat spreader structureto reduce hot spots and further help protect the lower stratum from theupper stratum operating heat or vice versa. FIG. 6D illustrates a twostrata 3D circuit 620 using techniques described herein. Furthermore,the through layer via (“TLV”) used to connect the upper stratum to thelower one could utilize titanium to further reduce the heat conductivitybetween these strata. These TLV could use extra thick isolation toreduce thermal conductivity to the surrounding areas. Additionally, someof those TLV may be dedicated thermal TLVs wherein their main functionis to serve as heat delivery channels to the heat sink and/or outsidesurface of the device. These even more important in respect to the TLVbeing used to conduct the heat from the operating circuit to the deviceexternal surface which is part of the device heat removal structure.Such extra thick lateral isolation could be greater than about 100 nm,greater than about 200 nm, greater than about 300 nm, greater than about500 nm or more than a micron thick.

In a 3D system such as is illustrated in respect to at least FIG. 6D orFIG. 11D-11E, may include both a memory array and a logic circuit, thethermal isolation 1157, to keep the logic heat away from the memoryarray, could be placed in between the logic circuit 1156 (or logiclayer) and the memory control circuit 1155 (or memory control circuitlayer) as is illustrated in FIG. 11E. In general many vias, such as ThruLayer Vias (TLVs), may be connecting between the memory control circuit1155 and the memory array 1131. These vias could connect tosubstantially every word-line, bit-line, source-line, and so forth. Onthe other hand the logic circuit 1156 could connect to the memorycontrol circuit 1155 using address lines which represent far lessconnections (as an example—10 address line could control, with properdecoder circuits, 1024 word-lines). Reducing the number of TLVs throughthe thermal isolation layer 1157 helps reduce the thermal connectivitythrough it and greatly improves the effective thermal isolation.

Formation of multiple levels of arrays of transistors or othertransistor formations in the structures described herein may bedescribed at least by the terms ‘multilevel device’ or ‘multilevelsemiconductor device.’ Some examples of multilevel device may includememory device such as DRAM, SRAM, and Flash memory and image sensorssuch as CCD and CIS.

3D devices could include redundancy for defect recovery in addition toredundancy techniques know for 2D devices. Such 3D devices could includeone-time-programmable memory for at least packaged level memory repair.Such redundancy techniques and structure has been presented in U.S. Pat.No. 8,395,191, incorporated herein by reference, in respect to at leastFIGS. 41, 86, 87, 114-132.

Additional variations of redundancy and repair techniques could beintegrated within the 3D SRAM. 3D DRAM or 3D NOR fabric as detailed inPCT/US patent application 16/52726 and U.S. application Ser. No.15/333,138, incorporated herein by reference. Hereinafter, the use of 3DNOR fabric in any of embodiment in this invention may be 3D SRAM fabricor 3D DRAM fabric unless otherwise specified.

Further inventive aspects follow. FIG. 7 illustrates a logic function ofgeneral ‘look up table’ and more specifically 3D architected look uptable LUT-U 702 being processed together on top of logic function LUT-B704, both sharing the same control gates and each may act as redundancyfor the other, where -U and -B respectively denote upper stratum andbottom stratum, or upper portion and the bottom portion of the 3Dstructure. FIG. 7 illustrates that the LUT-U is included in the upperstrata and the LUT is included in the bottom strata where two strata areconstructed the mean explained in this invention. Placement of thestratum may vary due to engineering and design considerations. Aprogrammable interconnect (I/C) structure 701 may include first I/Cstructure 706 and second I/C structure 707 which allow connecting eitherone of the logic function outputs, LU-Out 742 or LB-Out 744, to theprimary output 724. Such programmable interconnect may be SRAM or latch.Alternatively, such programmable interconnect may be antifuse based OTPor other non-volatile memory such as RRAM, EEPROM, or flash, dependingon the applications. The programmable interconnect may be implemented inthe fabric layers in between the upper and the bottom portion and couldbe considered as a third strata or comprise a portion of a thirdstratum. Self-test could be used to choose which of the outputs toconnect using the programmable connectivity structure first I/Cstructure 706 and second I/C structure 707. Redundancy could also beused for the interconnects such as is illustrated third I/C structure714, fourth I/C structure 716, and fifth I/C structure 717, which wouldconnect the LUT outputs to the secondary output 726. Another alternativeis to have redundancy of the support circuits 712 on the bottom of the3D NOR fabric as well.

FIG. 8 illustrates a redundancy scheme wherein a middle LUT-M 803 lookup table functions to repair faults in either the right LUT-R 802 or theleft LUT-L 804. The LUT-M, LUT-R, and LUT-L may be included at the samestrata. Alternatively, LUT-M, LUT-R, and LUT-L may be placed indifferent strata of the 3D chip. The right LUT-R 802 and the middleLUT-M 803 could share the same control gates, and the middle LUT-M 803and the left LUT-L 804 could also share the same gates disposed in thevalleys of the corresponding ridge as is illustrated. Programmableinterconnects structure 806, 807, 808, 814, 816, 817, 818, 827, 828allow connecting to selected LUT to the proper first primary output 824or second primary output 826 to function as two complementing LUTfunctions as discussed in respect to FIG. 23 of PCT/US patentapplication 16/52726.

These redundancy schemes have the advantage that they provide the repairlocally keeping the overall circuit functionality consistent with orwithout activating the redundancy function. These are especiallyimportant for logic circuit operation.

In these forms of redundancy read or write could be performed inparallel to two adjacent ridges once both ridge selects are enabled toaccelerate the redundancy operation.

FIG. 9A and FIG. 9B are corresponding to the 3D memory fabric presentedin FIG. 14B and FIG. 14C of PCT/US patent application 16/52726. Theyillustrate the designated 3D memory fabric such as 3D NOR structure forstaircase per layer connection 902 and the staircase contact holes 906.An alternative technique for staircase formation is illustrated inreference to FIG. 10A-10K. This technique leverages selective etch ratesbetween the layers forming the 3D multilayer substrate, such as in thecase of 3D NOR are the source/drain (S/D) layers, that could include N+type silicon, and the channel layers, that could include P type SiGelayers. Alternatively, the channel may be realized in the Si layerswherein the S/D substantially resides in N+ SiGe layers/regions. Theselective etch could be designed to etch the S/D layer faster than thechannel layer, for example, at a rate such as twice as fast or evenhigher than 2× such as (2-3)×, (3-4)× or even higher. This etch processis designed to be an isotropic etch, wet or dry etch could be used withproper consideration for sizes. However, this does not preclude the useof other etches, for example, one that is primarily but notsubstantially isotropic, and so forth.

Multiple etch processes have been developed providing selectivitybetween the silicon etch rate and the SiGe etch rate includingvariations related to the proportional content of Ge in the SiGe. Suchwork was reported by V. Loup et al in work titled “Silicon and SiGealloys wet etching using TMAH chemistry, published at Abstract #2101,224th ECS Meeting; by Borel, S., et al. “Isotropic etching of SiGealloys with high selectivity to similar materials.” Microelectronicengineering 73 (2004): 301-305; and by Stephan BOREL titled “Control ofSelectivity between SiGe and Si in Isotropic Etching Processes”published at Japanese Journal of Applied Physics Vol. 43, No. 6B, 2004,pp. 3964-3966, all incorporated herein by reference.

FIG. 10A illustrates the starting structure showing S/D layer that is tobe converted into a structure for staircase per layer access region,having a top layer 1002 of mask, and multilayer ridge of S/D layers 1004and channel layers in-between the S/D layers. The channel layer hereinthe per layer access region is a sacrificial layer that to be replacedby dielectric. The mask layer 1002 could be made to have a side etchsimilar to the S/D etch rate. The opening in the mask 1002 could besimilar to the depth of the S/D layer or few times larger. The widthcould be similar to the width of the ridge.

FIG. 10B illustrates the structure after etching through to top most S/Dlayer through the opening in the mask.

FIG. 10C illustrates the structure after etching the top most channellayer through the opening in the mask and through the top most S/Dlayer. It could be seen the top most S/D layer could be etched abouttwice the thickness (Z direction) of the channel layer to the sides (X-Ydirection) as the etching is isotropic and the etch rate of the S/Dlayer is twice higher than the etch rate of the channel layer.

FIG. 10D illustrates the structure after etching the second S/D layerthrough the top most channel layer. Note: These figures are not accurateand serve for illustrating the concept. FIG. 10K-FIG. 10N resulted fromsimulation and resemble the expected reality.

FIG. 10E illustrates the structure after etching the second channellayer through the formed opening.

FIG. 10F illustrates the structure after etching the third S/D layerthrough the formed opening.

FIG. 10G illustrates the structure after etching the third channel layerthrough the formed opening.

FIG. 10H illustrates the structure after etching the forth S/D layerthrough the formed opening.

FIG. 10I illustrates the structure after etching the forth channel layerthrough the formed opening.

Repeat the n-th S/D layer and n-th channel layer etch until the etchprocess reaches the desired bottom most S/D and channel layer.

FIG. 10J illustrates the structure after selective etch of the channelmaterial in the structure and replacing the channel layer with isolationmaterial. This process could accordingly form the desired staircase forper layer connection using one lithography step and multiple etch steps.Thus, top layer 1002 becomes etched top layer 1003, and the variousmultilayer ridge of S/D layers 1004 become the etched version 1005. FIG.10K-10N are process simulation charts illustrating such a stair-caseformation process. FIG. 10K may be the starting point having a resistprocessed to form a lithographic defined hole for the center of thestair-case structure. Other lithographic shapes may be formed due toengineering and design considerations. Herein, the SiGe was assumed tobe the channel layer and the Si was assumed to be S/D layer. FIG. 10Lmay be the first step of a multilayer etch using an isotropic etchhaving a SiGe: Si selectivity of 1:4. FIG. 10M illustrates the structureafter the etch process has reached the base silicon going through fiveSi/SiGe layer pairs. The staircase is now formed. FIG. 10N illustratesthe structure after removal of the photo resist and an optional cleaningetch with 100:1 SiGe:Si selectivity. The specific etch selectivity maybe adjusted based on engineering and design considerations. Manyvariations of this concept could be considered by an artisan insemiconductor process including changing the etch process between theselayers or even layer replacement techniques such as replacing thechannel layers. Controlling the isotropic etch of the S/D strips in theridge allows forming the desired staircase. Many options of materialswhich have different etch rates are well known in the art. An examplefor such could be found in a paper by Kirt R Williams et al, titled“Etch Rates for Micromachining Processing” published at JOURNAL OFMICROELECTROMECHANICAL SYSTEMS, VOL. 12, NO. 6, DECEMBER 2003incorporated herein by reference. The staircase formation techniquespresented in respect to FIG. 10A-10N could be adapted by an artisan insemiconductor processing to many of the 3D memory structures includingstructures that use multilayers of poly over oxide or tungsten overoxide.

FIG. 11A-FIG. 11D correspond to FIG. 35A-FIG. 35D of PCT/US patentapplication 16/52726. It is used to illustrates 3D system which includes3D-NOR fabric 1130 over ‘cut layer’ 1113 over substrate 1110, andbrought over from another substrate 1150 and cut layer 1143 peripherycircuits 1154, and brought over additional processing logic 1156enabling such as “Processing-in-Memory”, or “co-processor in memory” or“function in memory”. Such memory centric architecture may be usefulcompared to the conventional processor centric architecture for futuremachine learning, neural network, approximate computation and so forth.As discussed there many system options could leverage such 3D system‘Lego’. A generic memory array could be diced using predefined potentialdice lines or etch defined dice line to fit specific overlay logic, theoverlay logic itself could be broken to more than one stratum, and couldinclude dedicated stratum for I/O, cut from another generic wafer.Additional “Lego” options could be available from the 3D NOR fabric. Onesuch option is segmenting and allocating the number of layers into the3D NOR fabric and the amount of memory and programmable logicaccordingly. FIG. 11D illustrates one type of 3D NOR fabric 1130 withcontrol circuit 1154 and processing logic on top 1156. Alternativelyanother 3D system could be construct with similar “Lego” parts such asthe processing logic 1156 with modified control circuit 1155 and a 3DNOR fabric with much fewer number of layers 1131. Another type of systemvariation using similar ‘Lego’ parts is to modify within the 3D NORfabric where the thickness of the tunneling oxide is processeddifferently for sets of words line groups and accordingly creatingvariations with the memory type in the 3D system between retention timeand access time. Another type of structure variation that could beapplied is memory usage and the corresponding write and read techniquessuch as multilevel and mirror-bit tradeoffs between access time anddensity. Another type of modification that could be formed in the 3Dsystem is the allocation of the fabric to memory versus to programmablelogic. These variations could form completely different end 3D systemwith lower investment in new masks and higher leverage of the volume ofgeneric product produced in the process line.

An additional inventive embodiment for such a 3D system as isillustrated in at least FIG. 11D, is to add additional layer on top toprovide an electro optics circuit which could allow use of light, suchas, for example, fiber-optics or photonic components, to communicatewith other systems and for other systems to communicate to the 3D systemillustrated. Alternatively, the top layer of the 3D system may be imagesensors, hyperspectral sensor, or time-of-flight sensor. Such a 3Dsystem could comprise a memory fabric such as 3D NOR fabric 1130 whichcould be allocated as sub memory sections, some for high speed and somefor high density, and a compute circuits within control circuit 1154that could have many cores and control circuits designed forcommunications and control of the underling memory fabric (such as 3DNOR fabric 1130), and communication layer within processing logic 1156that could be made with material optimized for those tasks, such asthose optimized for RF. Such a 3D computer could be made to support veryefficient programming as all its internal routing are far shortercompared with current Printed Circuit Board (PCB) technique of computersystem integration or even the 2.5D/3D initiatives.

Such heterogeneous 3D integration allow the use of one type offabrication facility for one of the strata, for example, a memoryoriented fabrication facility to produce the memory array 1130, and verydifferent facility for a different stratum, for example, such as a logicorientated fabrication facility producing the memory control circuit1154, thus allowing an increased flexibility in the design of theoverall system including use of much more advance fabrication lines forsome of the stratum.

Use of the alignment technique we call ‘Smart Alignment’ allowsconnection between the upper strata and the lower strata with vias(Through Layer Via—TLV) that are as small as the thickness of the layerand the process capabilities allow. Such is useful for connecting memorycontrol circuits in one stratum to memory control lines such asbit-lines and word-lines on the other stratum.

FIG. 11F illustrates the “smart Alignment” technique. The target wafer1164, such as illustrated in FIG. 11B, could have its alignment mark1162 and a connection strip target 1160 along direction ‘X’ 1190, havinga length longer than the worst-case misalignment in ‘X’ direction of thewafer bonding (and subsequent release, planarization, and cleaningprocess). The transferred layer or wafer 1170, such as for examplecontrol circuit 1154 illustrated in FIG. 11A-11C, may have its owntransferred layer alignment mark 1166. The intersection between thehorizontal connection strip target 1160 and the designated upper stratumvertical connection strip 1172, which could be aligned to thetransferred layer alignment mark 1166, is now known and will beprocessed to be locating the TLV₂₁ 1168. The processed verticalconnection strip 1172 length should be designed to be longer than theworst-case misalignment in ‘Y’ direction of the wafer bonding.Accordingly, the via 1168 could be aligned, to target wafer alignmentmark 1162 in the Y direction and to the transferred layer alignment mark1166 in the X direction. Once the via layers are formed an upper layermetal mask aligned to the upper layer alignment mark 1166 could be usedto form connection between the transferred upper stratum and the targetstratum underneath. FIG. 11G illustrates connecting the upper stratumstrips 1178 to memory control lines 1176 in the target wafer using the‘smart alignment’ technique individually connecting to each controllines even for bonding misalignment which far exceed the memory controllines pitch.

Yet the target wafer 1164 in most cases of memory array would have atleast two set of control lines one in X direction and one in Ydirection. To allow effective connectivity the ‘Smart Alignment’technique could be enhanced to have two sets of TLV. One TLV₂₁ alignedto target wafer's alignment mark 1162 in Y direction and to thetransferred layer's alignment mark 1166 in X direction. And the otherTLV₁₂ aligned to target wafer's alignment mark 1162 in X direction andto the transferred layer's alignment mark 1166 in Y direction. This mayrequire two step of lithography. FIG. 11H illustrates such twoconnection sets. Bit-lines in X direction 1180 connected to upperstratum by strips in Y direction 1182 while word-lines in Y direction1184 connected to upper stratum by strips in X direction 1186.

An additional inventive embodiment relates to monolithic 3D by layertransfer whereby a unique structure may be formed by replacing siliconwith high quality oxide prior to the layer transfer at the time thathigh temperatures processes are acceptable. For example, the silicon inthe zone 1179 that is being designated for TLVs may be etched and filledin with high quality oxide (or a lower quality oxide deposition followedby a high temperature anneal) that would have leakage current of lessthan one picoamp per micron at a device power supply voltage of 1.5 andat a measurement temperature of 25° C. Thus, as well, the TLVs would notrequire any insulative lining to pass thru the TLV transiting layer,which could be islands/mesas of silicon in a sea of oxide, or viceversa.

An alternative to, two lithography steps with two via masks, could bethe smart use of direct write eBeam in which the eBeam alignment couldbe managed to provide proper placement for the TLV₁₂ and TLV₂₁.

In some applications, it could be desired to transfer stratum includinginterconnection performing what could be called parallel integrationinstead of sequential integration. Bonding layer or die in such casecould utilize hybrid bonding forming bonding and direct metal to metalconnection in the process. In general, such hybrid bonding utilizesconnection pads that are large enough to accommodate the bondingmisalignment which in advanced bonder is approaching 100 nm worst casemisalignment. Yet some memory stratum might use control line pitcheswhich could not accommodate the bonder misalignment. An alternative forsuch cases could be use of bonding oxide that could be made to conductby electrical signal, using what is known as One Time Programmable—“OTP”or Resistive RAM technologies. In such case one stratum could have somecontrol signal and power signal connected using the hybrid bonding whilethe memory control lines could be connected by programming.

FIG. 11I illustrates a section of memory control lines in one stratum.FIG. 11J illustrates connection segment on the other stratum. For thecase in which the memory stratum is the one under the connectionstructure of FIG. 11J includes connection strips in Y direction 1192that are formed long enough to cover the bonding misalignment in Ydirection, connected by via 1193 to the X direction connection wires1194 on the upper layer. FIG. 11K illustrates these connectionstructures after the bonding. For misalignment of less than three memorycontrol lines pitch, three independently controlled programming signalVP1, VP2, VP3 could be used to form the connection between the memorystratum and the logic stratum. These could be provided using properlyarranged and connected diodes. Other arrangements could be designed andengineered.

FIG. 12A and FIG. 12B correspond to FIG. 13E and FIG. 14D of PCT/USpatent application 16/52726. FIG. 12A illustrates an optionalalternating allocation of ridge select transistors 1202, 1203 formed inseries of the S/D lines on both ridge ends. The ridge select transistor1202, 1203 can allow selectively the specific S/D lines. FIG. 12Billustrates the ‘Y’ direction per S/D layer staircase structure 1204.FIG. 12C illustrates X-Y cut (top view) of such alternating ridge select1213 (RS1, RS3, RS5), 1222 (RS2, RS4) with ‘Y” oriented common staircaseaccess on both sides 1214, 1224. The ridge such as 1216 may beassociated with multiple word line controls (w1, w2, . . . ) which couldbe consider first gates w-1, and second gates w-2 and controllingchannel from both sides of the ridge, odd side w-1 o, w-2 o, and evenside w-1 e, w-2 e. FIG. 12D illustrates similar structure with aperspective 3D illustration of FIG. 12C except that the selecttransistors are staggered on left and right end of ridges. Sucharrangement of staggered select gates on left and right end of ridgesallows sufficient space for the per ridge select gate (without affectingthe adjacent ridge). FIG. 12E illustrates a variation on FIG. 12C inwhich the side of ridge with no ridge select 1217 is directly connectedto the respective ‘Y’ direction staircase structure 1214, yet isolatedfrom the ridge select of its adjacent ridge 1233. The isolation layer1233 may be a relatively thick oxide in order to minimize electrostaticcoupling from the gate and the ridge across the isolation layer 1233.So, the select gate would only control a ridge on its relatively thinoxide side. Such arrangement of select gate enables equivalent functionof FIG. 12C. The variation of FIG. 12E would allow access to each cellfrom both ridge ends, as there are both still connected to therespective staircase access 1214, 1224.

In consideration of the ‘smart alignment’ as was previously discussed inrespect to FIG. 11H, the 3D NOR fabric as is illustrated in FIG. 12Bcould be modified to allow easier connection to upper stratumaccommodating bonding misalignment in X and Y direction. FIG. 12Fillustrates such accommodation in modifying the structure of FIG. 12E.Two global wordlines (WL) are assigned for one local WL pitch; one forthe odd side and another for the even side of a single ridge. The globalword-lines WL1 1236 and WL2 1238 are oriented in the Y direction andcorrespond to Y direction word lines 1184. Alternatively, no global WLis used but each vertical local WL may be directly accessed by a 3Dstacked peripheral circuit on its top. The ridge select transistor 1228could be modified as illustrated in FIG. 12F to be extended in the Xdirection 1234 to accommodate X direction misalignment. Thus the ridgeselect transistor 1228 may be a long channel transistor, which improvesthe leakage behavior for an unselected ridge. The per level via 1205 ofFIG. 12B could be extended in the Y direction 1232 to accommodate Ydirection misalignment FIG. 12G is a 3D perspective illustration withextended gate length ridge select transistor 1244 corresponding to 1234.FIG. 12H illustrates the addition of connection vias, and FIG. 12Iillustrates adding the word lines 1246 and the extended per S/D layerconnections 1242. FIG. 12J illustrates side view of the extended per S/Dlayer connection. Precise wafer bonders available in the industry areproven and capable of bonding misalignments of less than 100 nm.Accordingly the structures to support such a bonder could be made withconnection pad of about 100 nm which could be used for ridge select pad1234 to be about 100 nm in the X direction and the per layer pad 1232 tobe about 100 nm in the Y direction.

Placing the staircase along the Y direction vertically aligned to theridge direction reduces the area overhead associated with per layeraccess. When combined with the 3D integration of memory control circuitstransferred and added on top and/or under the memory matrix, thissupports an array built from many micro-arrays each with its own memorycontrol circuits. Such a micro array or unit could have X directionand/or Y direction size of few tens of microns, or few hundreds ofmicrons. This arrangement reduces the capacitance and resistance of thememory control lines thus allowing lower power and higher speeds for thememory device.

Additional variation for the 3D NOR fabric is to use SiGe with 5% Gecontent for the S/D layers and SiGe with 20% or higher content for thechannel layers to achieve higher growth rate for the epitaxial growth ofthe multilayer structure which could be used for cost reduction oralternatively reduce epitaxial process temperature with lower effect onthe growth rate.

Additional alternative for the 3D NOR fabric is to utilize chargetrapping also as a variable memory function for brain type functionalityin a similar fashion to what have been proposed in PCT/US2016/052726 forthe RAM part of the fabric.

FIG. 18 of PCT/US patent application 16/52726, presents a programmingtable for the 3D NOR memory. It utilizes what is called Hot-Electroninjection. FIG. 13 of that same application depicts table for Flashmemory programming. It presents Fowler-Nordheim tunneling (“FN”) whichis a common flash programming and erasing technique and could allowlower energy per bit writing and erasing. Use of FN programming for NORtype flash memory is presented in a paper by Masayoshi Ohkawa et altitled “A 98 mm² Die Size 3.3-V 64-Mb Flash Memory with FN-NOR TypeFour-Level Cell” published at IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL.31, NO. 11, NOVEMBER 1996, incorporated herein by reference. The use ofFN tunneling as a programming mechanism may save write energy whencompared to the less efficient hot-carrier programming. The FN tunnelingcan be bit-specifically conducted for the presented 3D-NOR architecture.In an unselected ridge, the ridge-select gates are turned off so thatthe S/D lines become floating so to inhibit writing (programming) ofthose ridge memory cells. In a selected ridge, the ridge-select gatesare turned on so that the S/D voltages for writing or reading can beapplied through it. For the selected cell in the selected ridge, a highenough programming voltage is applied to the selected wordline and apair of S/Ds could be connected to a lower voltage, such as grounded, sothat there is sufficient electric field across the selected S/D line andthe selected wordline to effect charge transfer into the charge traplayer or into the floating gate. For the unselected cell in the selectedridge, a disabling high enough positive voltage could be applied to allunselected S/D lines to reduce the electric field across the unselectedmemory cells, and thus minimize program disturb. Note, under typical FNvoltages wherein the WL voltage for writing is assumed to be 20V, theinhibit voltage for the non-selected cell S/D could be ˜10V. Thehalf-selected cells are those cells that are sharing one of the selectedS/D lines and thus may suffer from disturb. The S/D lines could bedesigned to withstand such voltage differential to avoid source-to-drainbreakdown or punch-through from selected S/D line to the adjacentunselected S/D line Alternatively, the method is suitable for lower PGM(programming) voltages (assuming ˜5V), possibly adequate for thinnerO/N/O. Mirror bit techniques might not be useable with FN tunneling ordirect tunneling programming and some other disadvantages could beassociated with such FN or direct tunneling programming.

Despite the term “FN tunneling” solely appearing throughout here, itshould be understood that it is not intended to differentiate FNtunneling from direct tunneling, rather there is also contribution dueto direct tunneling as well as FN tunneling. Unless otherwise specified,the sole use of “FN tunneling” herein contains the meaning of directtunneling.

FIG. 13A illustrates a small section of the 3D NOR structure which couldassist in presenting alternative writing and erasing schemes of memorycells within the 3D NOR memory. Illustrating two columns, each with itslocal word-line, WL1 1304, WL2 1306, with 8 S/D lines 1311-1318, andRidge Select gate 1302.

The entire ridge could be Fowler-Nordheim (“FN”) erased by selecting theridge and either by grounding all S/D lines and channel while poweringall the word-lines with negative erase voltage −Ve, or by positivelybiasing the channel while grounding all S/D lines and WL's. Optionally,positively biasing S/D lines and grounding WL and Channel lines can becarried out as well. As discussed herein before, specific voltages couldbe set for specific structures. For example, −5 volts could be used forFN erase for −Ve, and +5 volts for Ve. For use of the channel access forany programming or erasing explained, the body contact structure needsto be disposed, which will be explained later herein.

Alternatively, the entire ridge could be hot-hole erased, by selectingthe ridge and grounding one S/D line from S/D pair and positivelybiasing the other S/D line while powering substantially all thewordlines with a negative erase voltage and optionally groundingsubstantially all channel lines. In this case, the hot-hole erasefavorably occurs near the positive biased S/D region. Therefore, suchhot-hole erase may be used to one-side ridge erase in a minor-bit memorysystem. In order to completely erase both the source side and the drainside storage nodes using hot carriers, the erase may be accomplished bytwo steps; one-side erasing followed by opposite-side erasing byswapping grounded S/D line and positively based S/D line.

A specific column within the ridge could be FN or direct tunnelingerased by having all the other word-lines at the same voltage as the S/Dlines while the selected column word-line would be at negativedifferential Ve. For example, such as grounding all the S/D lines (andchannel ‘body’ if such is used in the structure) and all thenon-selected word-lines and driving the selected column word-line withan erase voltage such as −5 volt in some specific structures.

FIG. 13B illustrates FN erase condition for one cell 1320. That cellword-line could be set to −5 v while the other column word-lines arekept at ground. The S/D line and channel ‘body’ of the selected cellcould be grounded while all other S/D and channel lines are leftfloating. In such FN single cell erase the adjacent cells (the halfselected cell) with the column 1322 might be disturbed and partiallyerased. All the other cells 1324 should be unaffected. The partiallyerased cell could be refreshed to their original state by per cell writesteps. Alternatively, the use module could be utilized only unaffectedcells such as using only the odd level cells. This would reduce thememory density while simplifying the operation of FN per cell erase.

The inverse of FN erase could be used for FN write (programming) soinstead of negative differential using a positive differential such as+5 v instead of −5 v of FIG. 13B. Accordingly the above discussion wouldapply to FN writing.

Many variations known for Flash memories could be applied and adapted tothe 3D NOR fabric. Such could be reversing the gate stack order byhaving the tunneling oxide between the gate and the charge trap layer.Such could be used for FN write and erase from the word-line to thecharge trap or the floating gate. Other variations could be engineeredby memory artisan using the techniques known in the flash memory art.

In general FN is known to be few orders of magnitude more efficient inpower then hot electron techniques, and accordingly preferred for manyapplications. Yet, the additional benefit of using Schottky Barriertechniques is its highly efficient hot electron programming, which couldbe effective enough for many of these applications. Additionally the useof SiGe for the channel with N+ silicon for the S/D, could provide anadditional enhancement to secondary hot electron injection as presentedin a paper by Kencke, D. L., et al. “Enhanced secondary electroninjection in novel SiGe flash memory devices,” Electron Devices Meeting,2000. IEDM'00. Technical Digest. International. IEEE, 2000. Thismechanism combines both the secondary electron injection with thesmaller bandgap to generate higher impact ionization rates andsubsequent electron injection probability. The proposed mechanisms maysignificantly reduce maximum voltages required for the program operationapplied to WL, S/D and channel lines.

The 3D memory structures shown in FIGS. 13C and 13D may includefloating-body devices, so the body potential may be stronglycapacitively coupled with the S/D line voltage. So, it is assumed thatwhen both S/D line voltages are positively raised up, the body potentialis also raised up accordingly. As a result, no sharp energy band bendingnear P-N junction is made to cause the band-to-band tunneling. It isassumed that the minimum voltage for FN tunneling erasing across thegate and the S/D line was −5V as shown in FIG. 13B. Therefore, thevoltage difference of −4 V across the gate and the S/D lines shown inFIG. 13C and FIG. 13D most likely will not cause the FN tunnelingerasing. However, the techniques illustrated in FIGS. 13C and 13D areintended for hot-hole injection caused by a potential gradient inducedby asymmetric voltage for one grounded S/D line and another partiallypositively biased S/D line along with a partially negatively biasedgate.

FIG. 13C illustrates Gate Induce Drain Leakage (“GIDL”) erase for onecell 1330 within a selected ridge 1332 wherein channel lines arefloating. The selected cell 1330 Source line 1352 could be grounded (0volt), its Drain line 1353 could be powered with positive voltage suchas 2 v, and its word-line 1334 is connected to negative erase voltagesuch as −2 v. The differential voltage between the positive Drain lineand the negative word-line (−4 v) should be below the voltage inducingFN erase. The specific voltage could be set for specific device asprevious discussed. The non-selected word lines 1336 could be groundedin order to disable GIDL current. The S/D lines above the selected cell1351 could be grounded and the S/D lines below the selected cell1354-1358 could be powered to positive 2 v. The non-selected cells 1344could therefore see their Source and Drain at same potential andaccordingly no current is induced to the channel and accordingly noncreation of hot-holes. And having the voltage difference across a gateand S/D line below the threshold level of FN tunneling should keep thetrap charge with no change. In the selected cell the differentialvoltage between its Source and Drain could induce leakage under thenegative gate bias, such leakage could form hot-holes, and the negativefield of the word-line 1334 will pull these holes into the charge trap(or floating gate) layer to erase its stored electrons charge.

Using positive voltage (+2 v) for the selected word-line 1334 of FIG.13C could allow writing in the charge trap (or floating gate) layer ofthe selected cell 1330. Having a positive gate would actually open theselected cell transistor strongly increasing the transistor current andaccordingly the formation of Hot-Electron to be pulled in by thepositive word-line voltage. Using the up side flip similar to FIG. 13Dcould change the location of trap charge. Note, the above mentionedvoltages are extremely small for typical NVM device and may be obtainedif extremely thin ONO thickness is selected, such as bottom-oxide of 1nm, nitride thickness of 2 nm and top-oxide such as 2 nm. Further, forCHE programming the drain to source voltage must be typically largerthan −3V. Other mechanisms such as SB injection may require lower drainvoltage (absolute value), such as −2V.

An alternative writing and erasing could be performed by having thenon-selected S/D lines floating. In order to use such a scheme, thefloating body 3D structure is preferred as the body region can be alsofloated according to the floated S/D.

As stated the specific voltages for write erase of selected cell and notaffecting of non-selected cells could be tuned for specific devices.These tuning could include the presented write and erase techniques andvariations of those as known in the flash memory art including mixingtechniques such as FN and Hot-Electron/Hot-Holes. Many variations areknown in the art and could be adapted for the 3D NOR memory. Such asthose presented in U.S. Pat. Nos. 7,113,431, 7,220,634, 7,590,005,8,183,616 and applications 2006/0125121, 2009/0086548, 2011/0095353 and2012/0231613, incorporated herein by reference. And papers such as byLei SUN et al. titled “Characteristics of Band-to-Band Tunneling HotHole Injection for Erasing Operation in Charge-Trapping Memory”published at Japanese Journal of Applied Physics Vol. 45, No. 4B, 2006,pp. 3179-3184, by Alvaro Padilla et al titled “Enhanced Endurance ofDual-bit SONOS NVM Cells using the GIDL Read Method” published at 2008Symposium on VLSI Technology, by Kyoung-Rok Han et al titled “5-bit/cellCharacteristics using mixed program/erase mechanism in recessed channelnon-volatile memory cells” published at Current Applied Physics 10(2010) e2-e4, by LIU LiFang et al, titled “A 1G-cell floating-gate NORflash memory in 65 nm technology with 100 ns random access time”published at SCIENCE CHINA, Information Sciences April 2015, Vol. 58, byYu Wang et al titled “A 65-nm 1-Gb NOR floating-gate flash memory withless than 50-ns access time” published at Chin. Sci. Bull. (2014)59(29-30):3935-3942, by Ken Uchida et al titled “Enhancement ofhot-electron generation rate in Schottky sourcemetal-oxide-semiconductor field-effect transistors” published at AppliedPhysics Letters 76, 3992 (2000); by Kyeong-Rok Kim titled “Design of NORflash memory cells, with high speed programming by utilizing anasymmetric Silicide(TiSi2) Drain” published at ICASIC07, by E. J. Prinzet al titled “90 nm SONOS Flash EEPROM Utilizing Hot Electron InjectionProgramming and 2-Sided Hot Hole Injection Erase” published at NVMWorkshop 2003, by Li-Jung Liu et al titled “Performance enhancement inp-channel charge-trapping flash memory devices with Si/Ge super-latticechannel and band-to-band tunneling induced hot-electron injection”published at Thin Solid Films 533 (2013) 1-4, by Choi, Sung-Jin, et al.“A novel TFT with a laterally engineered bandgap for of 3D logic andflash memory,” published at VLSI Technology (VLSIT), 2010 Symposium,IEEE, 2010, and by Yu-Hsien Lin et al, titled “Band-to-Band Hot HoleErase Mechanism of p-Channel Junctionless Silicon Nanowire NonvolatileMemory” published at IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 15, NO.1, JANUARY 2016, all incorporated herein by reference.

The silicidation process suggested in PCT/US patent application 16/52726and U.S. application Ser. No. 15/333,138 could be done by knowntechnique in the art. These could include two annealing steps. First toform the metal penetration into the silicon followed, then removal ofthe excess metal by dry or wet etch, followed by second anneal toactivate the silicide metal. These processes could include microwaveannealing which was demonstrated to allow reduced temperature. Suchprocess has been presented in papers such as by Xiangbiao Zhou et altitled “Schottky Barrier Height Tuning via Nickel Silicide as DiffusionSource Dopant Segregation Scheme with Microwave Annealing” published at15th International Workshop on Junction Technology (IWJT), by Shih,Tzu-Lang, and Wen-Hsi Lee. “High Dopant Activation and DiffusionSuppression of Phosphorus in Ge Crystal with High-TemperatureImplantation By Two-Step Microwave Annealing” ECS Transactions 72.4(2016): 219-225, by Chun-Hsing Shih et al titled “Metallic Schottkybarrier source/drain nanowire transistors using low temperaturemicrowave annealed nickel, ytterbium, and titanium silicidation”published at MSSP 16, by Sounak K. Ray et al titled “Enhanced chargestorage characteristics of nickel nanocrystals embedded flash memorystructures” published at Journal of Experimental Nanoscience, 2013 Vol.8, No. 3, 389-395, by Chaochao Fu et al titled “Schottky Barrier HeightTuning via the Dopant Segregation Technique through Low-TemperatureMicrowave Annealing” published at Materials 2016, 9, by Jian Deng et altitled “A modified scheme to tune the Schottky Barrier Height of NiSi bymeans of dopant segregation technique” published at Vacuum 99 (2014)225e227, by Y.-J. Lee et al. titled “Record-Thin 10.5 nm Ni SilicideFilm for 2012-2021 by Two-step Low Temperature Microwave Anneal”published at IEDM 11; Y.-J. Lee et al. titled “Full Low TemperatureMicrowave Processed Ge CMOS Achieving Diffusion-Less Junction andUltrathin 7.5 nm Ni Mono-Germanide” published at IEDM 12; by Y.-J. Leetitled “A Novel Junctionless FinFET Structure with Sub-5 nm Shell DopingProfile by Molecular Monolayer Doping and Microwave Annealing” publishedat IEDM 14; by Y.-J. Lee et al. titled “Low-Temperature MicrowaveAnnealing Processes for Future IC Fabrication—A Review” published inIEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 61, NO. 3, MARCH 2014; by T.Yamaguchi et al. titled “Low-Resistive and Homogenous NiPt-SilicideFormation using Ultra-Low Temperature Annealing with Microwave Systemfor 22 nm-node CMOS and beyond,” published at IEDM 2010; by Ming-KunHuang et al. titled “Dopant segregated Schottky barrier nanowiretransistors using low-temperature microwave annealed ytterbium silicide”published in Japanese Journal of Applied Physics 53; and by Ming-KunHuang et al., titled “Dopant segregated Schottky barrier nanowiretransistors using low-temperature microwave annealed ytterbium silicide”published in Japanese Journal of Applied Physics 53, 116501 (2014), allof the forgoing are incorporated herein by reference. Equipment forMicrowave Annealing has been offered by DSG technologies of California.An additional advantage for use of Microwave Annealing and ALD is thecompatibility of these processes with 3D structures. For example, thelaser annealing might deliver non-uniform energy along the depth of themultiple stacks of semiconductor layers, which may result innon-uniformity. Microwaves could be designed to penetrate inside thesemiconductor so that the annealing result may be uniform across themultiple stacks of semiconductor layers. In addition, the metal ALD mayfurther enhance the metal silicidation, as the metal ALD can enable adeposit of a precise amount of metal to be used for the silicidation.Consequently, no residual metal unreacted with the silicon may left andthereby no subsequent residual metal removal may be necessary. In someembodiments, the exact amount of the layered metal may be fully consumedduring the silicidation process, which could save the subsequent removalprocess of non-reacted metal. Such could be also effective foradditional applications such as FinFET and nano-wires providingadditional advantage to reduce Schottky Barrier variations.

FIG. 14A presents a drain current versus gate voltage (Id-Vg) curvetaken from FIG. 8 of the paper by Ming-Kun Huanget et al. It illustratesthe advantage of microwave annealing of a silicided nano-wiretransistor. The chart illustrates the advantage of Dopant Segregationfor Schottky Barrier in respect to reducing ambipolarity withoutsacrificing the drive current. Yet in some alternatives a 3D NOR memorystructure could be made with transistors having some level ofambipolarity. In such cases the sense amplifier could be made to supportimproved memory function. Assuming that the chart related to SchottkyBarrier 1402 represent the memory cell of such 3D NOR. Assuming that theVT shift effected for ‘0’ state is 1 v while ‘1’ state is as plotted inFIG. 14A. The sense amplifier for read circuit could be made to sensesthe differential drain current for gate voltage of 2 v and 0 v. Forstate ‘1’ such differential current could be about 10⁻⁶ A, while forstate ‘0’ the differential current could be about 10⁻⁷-8*10⁻⁸ 2*10⁻⁸ A.Accordingly such differential sense amplifier could enable range ofmemory transistors to effectively function.

FIG. 14B is an Id-Vg curve taken from FIG. 11. (b) of a paper by Liu,Yongxun, et al., “Comparative Study of Charge Trapping Type SOI-FinFETFlash Memories with Different Blocking Layer Materials,” Journal of LowPower Electronics and Applications 4.2 (2014): 153-167, incorporatedherein by reference. It illustrates that in some memory applications aself-reference differential sense amplifier could be an effectivetechnology for sensing the memory information. For example, if the Iddifferential read is determined by two step gate biasing between Vg₂=4 vand Vg₁=0.5 v, then in the erase state the differential Id is relativelylarge compared to the programmed state. Accordingly such self-referencedifferential sense amplifier could be a useful memory sensing techniquefor memory structure presented herein and elsewhere. Setting the gatevoltages for such detection technology could be so the memory transistorthreshold voltage (Vt) is in the voltages range (Vg1<Vt<Vg2) for onememory state and out of it (Vg1>Vt or Vt>Vg2) for the other. Suchself-reference differential sensing could be effective in reducing theeffect of absolute Id current value that is not related to the change inthat cell wordline voltage.

An additional inventive embodiment is to reduce the ambipolarity effectby using a relatively reduced drain to source voltage (V_(DS)) such as0.5-1 V during the read operation (for example, as compared to state ofthe art Minor-bit technology of 1.4-1.6 V). Lowering drain voltage cansuppress the band-to-band tunneling leakage causing ambipolarity. Thus,effectively reducing the ambipolar current of the unselected bitlinecell during the reading of the selected wordline cell. The reducedV_(DS) may still distinguish between two physical bits per cell such asminor bit scheme in reverse and forward read operations when a small Vtshift between the programmed and the erased states such as about 1 voltmay be implemented and as a narrow charge distribution is obtained usingSB or DSSB injection compared to Channel Hot Electron injection in dopednp junction. Furthermore, the reduced V_(DS) improves immunity to readdisturb and extends the retention time and endurance of the memorytransistor.

The Dopant Segregation Schottky Barrier (“DS-SB”) formation processsuggested in PCT/US patent application 16/52726 in respect to at leastFIGS. 8E and 41E, could be modified to allow broader device control.FIG. 15A illustrates a Y-Z cut-view of two level 3D NOR memory(resembling FIG. 2 of 16/52726). On top of a section of a carrier wafer1500, illustrated are side view of two ridges, having two layer ofmemory having channels 1502, 1504 each between two S/D regions 1501,1503 and 1506. A hard mask portion on top 1508 that could have been usedfor the etch mask forming these ridges. The S/D regions 1501, 1503 and1506 could be made of N+ doped silicon and the channel 1502, 1504 couldbe made with P doped SiGe, or many other variations including replacingthe NPN with PNP SiGe with Silicon etc. For the following processalternatives, the materials of the channel 1502, 1504 could beselectively or non-selectively isotropic etched in respect to the S/D1501, 1503, 1506 in order to create selective indentation. FIG. 15Billustrates the structure after a selective isotropic etch of thechannel regions 1505. For the case in which the S/D is N+ silicon andthe channels are P type SiGe the selectivity could be applied to about100:1 as is illustrated in FIG. 1. FIG. 15C illustrates the structureafter deposition of protective isolation 1510 such as silicon dioxidefollowed by directional etch using the hard mask 1511 to removeprotective isolation on S/D side walls while leaving the protectiveisolation 1510 only at the region of the etched away SiGe. The structureis now ready for the extra S/D diffusion doping and S/D silicidation.The protective isolation could be later replaced with O/N/O (TunnelingOxide/trapping Nitride/isolation Oxide) or be already design to be usedas at least part of the O/N/O structure. In this step, the processtemperature may be determined with consideration that doesn'tsubstantially impact on the silicide and avoid junction spike.

Adding the metallic material for the silicidation could be done by knownin the art deposition techniques, for example, such as ALD. Examples maybe found in a paper by Hyungjun Kim, titled “Atomic layer deposition oftransition metals for silicide contact formation: Growth characteristicsand silicidation” published at Microelectronic Engineering 106 (2013)69-75; in a paper by Viljami Pore et al. titled: “Nickel Silicide forSource-Drain Contacts from ALD NiO Films” published at the InterconnectTechnology Conference and 2015 IEEE Materials for Advanced MetallizationConference (IITC/MAM), 2015 IEEE International; and by Jinho Kim et al.titled “Characteristics of Nickel Thin Film and Formation of NickelSilicide by Remote Plasma Atomic Layer Deposition using Ni(iPr-DAD)2”:published at Journal of the Korean Physical Society, March 2015, Volume66, Issue 5, pp 821-827; and by Kinoshita, A., et al. “Solution forhigh-performance Schottky-source/drain MOSFETs: Schottky barrier heightengineering with dopant segregation technique,” published at VLSITechnology, 2004. Digest of Technical Papers. 2004 Symposium on. IEEE,2004, all of which are incorporated herein by reference.

An embodiment of the invention is to form full metallic source/drains.Such could include tuning the Schottky Barrier height or Fermi levelde-pinning by a very thin deposition of isolation, for example, such assilicon oxide or high-k dielectric, prior to the deposition of metal.Such could be achieved by first fully etching away the S/D regions andthen filling in, the isolation using deposition techniques such as ALD,followed then by metal deposition and completed by removing the excessmetal using etching, for example, anisotropic etching. Such techniquesare known in the art as Metal Isolation Silicon (“MIS”). Such has beenpresented by Connelly, Daniel, et al. in a paper titled “A new route tozero-barrier metal source/drain MOSFETs,” published in IEEE transactionson nanotechnology 3.1 (2004): 98-104; by Demaurex, Bénédicte in adissertation titled “Passivating contacts for homojunction solar cellsusing a-Si: H/c-Si hetero-interfaces.” at ÉCOLE POLYTECHNIQUE FÉDÉRALEDE LAUSANNE, 2014; by Chiu, Fu-Chien titled “A review on conductionmechanisms in dielectric films,” published in Advances in MaterialsScience and Engineering 2014 (2014); and B. E. Cossa, et al. in a papertitled “CMOS band-edge schottky barrier heights using dielectric-dipolemitigated (DDM) metal/Si for source/drain contact resistance reduction”VLSI Technology 2009, pp. 104-105; all of the forgoing are incorporatedherein by reference. The full metal source/drain to channel junction canbe formed on one or more well-defined crystallographic orientationsurfaces of the semiconductor channel as referenced in U.S. patentapplication publication 2010/0065887, incorporated herein by reference.Such approaches may be used to control the effective Schottky Barrierheight. The metal source/drain can include a single type of metal suchas tungsten, cobalt, platinum, nickel, or their silicide. Alternatively,the metal source/drain may include a stack of multiple metals in orderto form a desired metal work-function and thereby a specific effectiveSchottky Barrier height. Alternatively, the stack of multiple metals maybe used where the first metal contacts the semiconductor channel isthin, but predominately defines the effective Schottky barrier heightand the subsequent metal(s) may be chosen for process convenience. Forexample, such as is disclosed in U.S. patent application publication2011/0008953, incorporated herein by reference. For the memoryapplication as presented herein the Schottky Barrier could be tuned toabout 0.1-0.5 eV. Alternatively, the multilayer substrate, such as isillustrated in FIG. 3A of PCT/US16/52726, could be made with undoped orP doped silicon designated to become the memory channel while the S/Dlayers could be first be made of sacrificial SiGe to be replaced withmetal and function as the S/D of the memory structure, effectivelyexchanging the role of the silicon and SiGe in the structure. Avariation of such a sacrificial SiGe flow could include doping thebottom most and the upper most of the silicon strips after the removalof the SiGe strips. Such doping could use techniques such as solid phaseor gas based diffusion or monolayer doping (MLD), as previouslydiscussed. Such could be used to form N+ regions in the silicon formingNPN type vertical transistors, and by adding metal into the grooves leftby the removal of the SiGe the S/D lines could be completed reducing thebit lines resistivity, and could include forming DSSB vertical memorycells.

FIG. 15D illustrates an alternative in which the structure of FIG. 15Bis formed via a two-step etch; selective SiGe etch followed bynon-selective isotropic etch, etching both the S/D and the channel atabout equal rate, which create notch near Si and SiGe corners. Theresults should have round corner unlike what is in FIG. 15Dillustration. The channel region 1516 are narrowed further but the S/Dregions are also etch forming an S/D neck 1514 regions for the spaceetch from the side that was open by the prior channel etch, and athinner S/D 1512. The height of the neck 1514 in Z direction could becontrolled by the etch depth of this second etch step. FIG. 15Eillustrates the structure of FIG. 15D after similar formation ofprotective isolation 1520. Since the protective isolation 1520 isextended over the junction near the S/D 1521, the silicidation junctiondirect short with the channel may be substantially avoided while thesilicidation proceeds along the S/D sides. The protective isolationcould be later replaced with O/N/O (Tunneling Oxide/trappingNitride/isolation Oxide) or be already design to be used as at leastpart of the O/N/O structure. In this step, the process temperature maybe determined with consideration that doesn't substantially impact onthe silicide and avoid junction spike. The top most S/D 1521 could beused as mask for excess protective isolation directional etch removal.Alternatively, the hard mask 1508 could be trimmed to guarantee the S/Dside wall exposure for the following silicidation. This second etch stepallow forming a neck to the S/D providing more control for the DS-SBformation.

An additional inventive embodiment is an additional alternative for the3D NOR formation process, wherein it use a multilayer in which the S/Dlayers are kept un-doped prior to the subsequent silicidation process.Such undoped S/D layer and S/D doping last process can prevent thechannel autodoping problem during a multilayer epitaxial growth process.For the SB type that would be fine as the S/D are defined by thesilicidation process. For other types of memory cells and for DSSB themoderate N concentration such as order of 10¹⁶/cm3 or higherconcentration of N+ dopant such as higher than 10²⁰/cm³ could beselectively added to the S/D region. which could be silicided after theridge formation. In these cases, the channel regions could first beprotected by techniques similar to those in reference to FIG. 15C-15Eherein. Solid phase or gas base diffusion could be used to dope thevertically arranged multiple layers though the exposed S/D regions. Anexample of these types of doping techniques are presented in papers byAjay Kumar Kambham et al. titled “Three dimensional doping and diffusionin nano scaled devices as studied by atom probe tomography” published inNanotechnology 24 (2013) 275705 (7pp); by Thomas E. Seidel titled“Atomic Layer Deposition of Dopants for Recoil Implantation in finFETSidewalls” published at Ion Implantation Technology (IIT), 2014 20thInternational Conference on Ion Implantation; and by U.S. patent U.S.Pat. No. 5,891,776, and by D. Raj titled “Plasma Doping of High AspectRatio Structures” published at Ion Implantation Technology (IIT), 201420th International Conference on Ion Implantation; all of the forgoingincorporated herein by reference. A similar technique is also calledMono Layer Doping (MLD) as presented by Ye, Liang, et al. “Doping ofsemiconductors by molecular monolayers: monolayer formation, dopantdiffusion and applications.” Materials science in semiconductorprocessing 57 (2017): 166-172, all are incorporated herein by reference.These techniques could be used with substantially every 3D memoryherein. For example, MLD techniques could be used on a dedicated regiondesignated for S/D or on the outer side of a region designated aschannel. It could also be used for DSSB formation.

The epitaxial process forming the multilayer base structure of the 3DNOR formation process could utilize an alternative technique to reducethe probability of dopant transition from the future S/D regions to thechannel regions. In a paper by Robert J. Mears et al. titled“Punch-Through Stop Doping Profile Control via Interstitial Trapping byOxygen-Insertion Silicon Channel” presented at EDTM 2017, incorporatedherein by reference, an ultra thin layer of oxide integrated in theepitaxial process is suggested to keep dopant from drifting or diffusingby heat. A mono layer or even less than monolayer of oxide is aneffective barrier to dopant pass through. Accordingly, for themultilayer epitaxial process, such oxide blocking could be integrated tosupport in-situ doping of the S/D regions with blocking oxide at theinterface of the S/D layer to the channel layer. Such a method should becarefully considered as it may degrade SB current performance if SBtechnology is to be implemented.

As note previously, the role of S/D and Channel may be replaced whereinSi serves as the channel and SiGe as the S/D region. Further and inaccordance with 15A-E, SiGe may be completely selectively etched whereintop and bottom planes of silicon layers may be doped by various methodssuch as Molecular Monolayer Doping, thus forming both channel and S/Dregion within the Silicon crystalline layer.

A known concern with memory arrays is various types of disturbs. Some ofthose are related to parasitic capacitance and similar forms of signalcoupling due to the relatively long and close proximity of parallelmemory control lines such as bit lines and word lines. These concernsare part of the engineering challenge of any memory device and could beincluded in the engineering of a 3D NOR memory structure. Some of thealternative techniques in the following could be adapted for such memoryengineering.

A body contact as discussed in respect to FIG. 42A-42E of PCT/US16/52726could be engineered either at the edge of a memory unit or multipletimes along the ridge. The connection lines (4248 of PCT/US16/52726)could be called body-lines and could be connected to ground, or to a‘body control’ which could be connected to a specific voltage control aspart of the memory control circuit and logic. Such ‘body control’ couldbe set to a positive voltage to assist the memory erase step. In someembodiments, a positive body voltage erase may be accomplished with theground voltage to the selected word lines, eliminating the need of anegative voltage for all operations, thus as a result the periphery area(memory control circuits) used for a negative voltage generator can besaved. In some applications it could be combined with higher doping inthe center of the channel, for example, such as indicated in FIG. 1B asSi_(0.8)SiGe_(0.2), to improve the body horizontal conductivity.

An additional embodiment is to have within a selected ridge all of theunselected S/D lines left floating (e.g. FIG. 13B), which may beconnected together, for example, through a multiplexer in the peripherycircuits. By connecting together all the S/D lines left floating, theywill form a much larger capacitive load thus significantly reducing thecapacitive coupling to the two active S/D lines.

An additional embodiment, such as when using in FN or direct tunneling,is to sequence the writing sequence to reduce cross talk by firstactivating the selected Source and Drain (the two adjacent S/D lines),then assert the selected word-line to turn on the vertical transistor ofthe selected bit cell. Then after the cross-talk ripple to adjacent S/Dlines has subsided, move the wordline bias high enough so that thewriting process will be effective only in the selected memory cell, thusreducing the disturb effect.

An additional embodiment is a 3D NOR structure alternative: to replacethe full ridge shared body contact with a per layer body contact using astair-case to allow selective access control for each body layer. FIG.15F illustrates such structure in which the body between S/D1 and S/D2could be controlled by signal B1, the body between S/D2 and S/D3 couldbe controlled by signal B2, and so forth. In such a 3D NOR structure, analternative writing technique could be achieved by using one word-linesuch as WL1 and one body layer of a selected ridge, such as B2, toselect a specific cell 1540. Using FN tunneling or direct tunneling byhaving the voltage difference between B2 and WL1, for example using apositive voltage for the selected WL and zero or a negative voltage forthe selected channel ‘body’ line will pull charge into the relatedcharge trapping region. All S/D lines may be left floating. For theerasing operation using a positive body contact voltage, all S/D linescould be left floating while the selected WL is grounded and theremainder of the WL's floating. Alternatively, the aforementionedconfiguration of sharing voltages between selected WL and Channel linesmay benefit by requiring a smaller voltage range to perform program anderase operations. Such maybe accomplished by negative half of erasingvoltage to the gate and positive half of erasing voltage to the body tocreate a full erase voltage across the gate and the body while all S/Dlines could be left floating. Furthermore, inhibit of non-selected cellsis obtained naturally. Alternatively, to avoid the need of negativevoltages and associated array size penalty, only positive voltages maybe utilized. Programming operation using only positive word linevoltages is accomplished by grounding the channel line and all otherunselected channel lines are left floating. The unselected S/D linescould be biased by half voltage of the programming word line voltage sothat the voltage difference between the selected word line andunselected cells is low enough to avoid any undesired FN tunneling.Alternatively, for programming operations using a positive word linevoltage, the unselected S/D lines could be left floating oralternatively biased by half voltage of the programming word linevoltage so that the voltage difference between the selected word lineand unselected S/D line is low enough to avoid any undesired FNtunneling from the S/D lines. The selected body voltage to the selectedchannel B2 should be selected per ridge to avoid writing in thenon-selected ridge. An additional embodiment in respect to such form ofwriting is to steer the charges to be close to one of the S/D lines suchthat at least two charge locations could be formed to increase thememory density. Such could be done for example by having S/D3 at groundwhile all other S/D lines are floating, preferably shorted together. Theelectric field between the negative body B2 and the grounded S/D3 duringprogram operation wherein also a positive voltage is applied on WL'scould pull the electrons toward the S/D3 side for writing on that sideof the charge trap region and for the other side replace roles withS/D2. Accordingly, the storage locations per facet could be madeeffective with such a writing technique. Additional variations couldinclude a blend by combining FN type writing with some level of hotelectron by proper voltage control of S/D2 and S/D3. An additionalalternative for charge steering could include modulating the steeringS/D line by a wavelet function similar to what has been presented in atleast U.S. application Ser. No. 15/333,138 with respect to at least FIG.27 to FIG. 32.

FIG. 15G is an Y-Z cut view illustrating an optional alternative to astaircase for forming a per layer ‘body’ contact presented in respect toFIG. 15F herein with reference to B1-B7. It illustrates a pillarelectrode 1558 to form a programmable connection per layer throughprogrammable isolation 1556 such as a one-time programmable antifuse,for example, formed with silicon oxide or other resistive switchingmaterial that could be electrically programmed to form a conductiveconnection from the pillar electrode 1558 to the designated body such asbody 1564. The side view illustrates S/D lines that could be referred asS/Dn+2 1552, S/Dn+1 1560, S/Dn 1568 and S/Dn−1 1570. The designatedchannels to form a programmable connection to, are illustrated as 1562,1564, 1566 for which 1564 could be considered as the ‘body’ for channel‘n’. During the formation of the structure, the S/D protectiveisolations 1550, 1554 could be processed in a similar way to the processused to form channel protection 1510. The structure illustrated in FIG.15G could be designed to form enough vertical pillars 1558 to allow atleast one pillar per body. Then the per layer contacts to the S/D linescould be used to program the connection between the vertical pillarelectrode 1558 to the designated body. Such programming could be formedby pulsing +Vpp to the vertical pillar 1558 and −Vpp/2 to S/Dn andS/Dn+1 resulting in forming programmable link 1580 between the verticalpillar electrode 1558 and the Channel n body 1564. The adjacent S/Dn−1and S/Dn+2 could be pulled-up as additional protection. The verticalconnection illustrated in FIG. 15G could also be made oriented in Ydirection parallel to the connection structure for the S/D lines as isillustrated in FIG. 12B.

An additional alternative when the memory structure includes body accessis to use the programming method known as Channel Initiated SecondaryELectrons injection (“CHISEL”) which could allow lower writing voltages.For example, the Source line could be held at Vs=0 v the Drain at Vd=2to 3 v and the ‘body; at Vb=−2 to −3 v. Such programming techniques hasbeen detailed in a paper by Mahapatra, Souvik, S. Shukuri, and JeffBude. “CHISEL flash EEPROM. I. Performance and scaling,” IEEETransactions on Electron Devices 49.7 (2002): 1296-1301; by Mahapatra,Souvik, S. Shukuri, and Jeff Bude. “CHISEL flash EEPROM. I. Performanceand scaling,” IEEE Transactions on Electron Devices 49.7 (2002):1296-1301; by Driussi, Francesco, David Esseni, and Luca Selmi.“Performance, degradation monitors, and reliability of the CHISELinjection regime” IEEE Transactions on Device and Materials Reliability4.3 (2004): 327-334; by Nair, Deleep R., et al. “Explanation of P/Ecycling impact on drain disturb in flash EEPROMs under CHE and CHISELprogramming operation” IEEE Transactions on Electron Devices 52.4(2005): 534-540; and by Stefanutti, Walter, et al. “Monte Carlosimulation of substrate enhanced electron injection in split-gate memorycells.” IEEE Transactions on Electron Devices 53.1 (2006): 89-96, all ofthe forgoing are incorporated herein by reference.

The memory structure herein was presented as a charge trap memory. Whenthe target application could make tradeoffs between write speed andretention time, the charge trap layer may be tuned accordingly. Asillustrated in IEEE ELECTRON DEVICE LETTERS, 16, 11, p. 491, 1995 by H.Clement Wann and Chenming Hu, “High-Endurance Ultra-Thin Tunnel Oxide inMONOS Device Structure for Dynamic Memory Application”, while thinningdown the bottom-oxide thickness improves program speed, retention timedecreases significantly. An alternative approach may be consideredwherein the bottom-oxide may be replaced with low-trapping nitride suchas oxinitride as published in Masayuki Terai, Koji Watanabe, and ShinjiFujieda, “Effect of Nitrogen Profile and Fluorine Incorporation onNegative-Bias Temperature Instability of Ultrathin Plasma-Nitrided SiONMOSFETs”, IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 54, NO. 7, JULY2007 or JVD nitride as published in IEEE ELECTRON DEVICE LETTERS, VOL.21, NO. 11, pp. 540 2000, by Yee Chia Yeo, Qiang Lu, Wen Chin Lee,Tsu-Jae King, Chenming Hu, Xiewen Wang, Xin Guo, and T. P. Ma, “DirectTunneling Gate Leakage Current in Transistors with Ultrathin SiliconNitride Gate Dielectric”. For a similar retention time, such a layer mayprovide better control of ONO formation as the required thickness issignificantly larger, directly related to the ratio of dielectricconstants, 7/3.9. Such an advantage may be realized with very a thinnitride layer of about 1 nm which may be production worthy compared ˜0.6nm silicon-oxide which may not feasible to realize in a productionenvironment. An additional advantage is a faster FN erase speed thanksto the significantly smaller offset in valence band with respect to thesilicon. Such a method may therefore enable an erase operation and limiterase voltages to lower or similar values as the program voltage.Program speed may also be improved significantly thanks to the smallerband offset if a hot electron injection mechanism is utilized. Such amethod may be Channel Hot Electron Injection (CHEI) or Channel HotInjection Secondary Electrons (CHISEL) in doped np junctions oralternatively in Schottky Barrier or DSSB transistors hot electrons aregenerated next to the source wherein injection also takes place. Furtherimprovement in program and erase speed or voltages may be brought aboutby thinning down to about 2 nm the trapping nitride layer which may beformed either by LPCVD or ALD methods with a potentially significantprogram window of 1-2V as referred in IEEE ELECTRON DEVICE LETTERS, VOL.32, NO. 11, p. 1501, 2011 by G. Van den bosch, G. S. Kar, P. Blomme, A.Arreghini, A. Cacciato, L. Breuil, A. De Keersgieter, V. Paraschiv, C.Vrancken, B. Douhard, O. Richard, S. Van Aerde, I. Debusschere, and J.Van Houdt, “Highly Scaled Vertical Cylindrical SONOS Cell With BilayerPolysilicon Channel for 3-D NAND Flash Memory”. Other forms of suchmultilayers could be engineered to fit the specific design objective ofretention vs. write time.

An additional option is to use the low trapping nitride, such asoxynitride and Jet Vapor Nitride mentioned above, as a replacement tothe high doping charge trapping nitride layer, thus realizing a layerwhich accommodates injected charges in the conduction band of the lowtrapping nitride. Such a method would be an alternative approach to thecommon industry standard of floating gate polysilicon.

The memory structure herein was presented as a charge trap memory.Recently good progress has been made in respect to ferroelectric typememories, especially in respect to utilizing Hafnium Oxide and ZirconiumOxide based materials (HfO, ZrO, HfZrO, ZrSio, . . . ). These memoriesare referenced as FRAM and could provide higher write and erase speedscompared to charge trap based memories. At the current time adevelopment effort is being pursued by the industry to develop such FRAMtechnology to be commercially viable. The technologies in developmentfor such FRAM include advanced ferroelectric deposition techniques suchas ALD. Adapting FRAM to the 3D-NOR fabrics presented herein could be agood option. These could include also a mix, in which some of theregions are processed with O/N/O and some of the other regions with FRAMmaterials such as HfO₂ and silicon doped HfO2 (Si:HfO2) or Zr doped HFO₂based materials. For example, the locations where the O/N/O layer usedto be formed can be replaced with a stack of dielectric to function as aferroelectric memory transistor. Alternatively, such locations mayinstead be formed with a stack of a charge trapping layer and aferroelectric layer. Such a mix could be attractive for many systems asit provides multiple memory technologies, low power, and time fortransferring data between these memory technologies as was discussedherein. Using FRAM within the 3D-NOR memory could include many of thevariations referred herein in respect to charge trap memories. Thesecould include multi-level cells in which multi-bits are coded in viadifferent writing voltages or different write times. These could alsoinclude multi-bit locations similar to minor bit and multi-gatessteering of bit location such as discussed in respect to at least FIG.10E of PCT/US16/52726 and FIG. 15A to FIG. 23 of U.S. Ser. No.15/333,138 Similar to charge trap, FRAM is an electric field basedmemory and is an isolative material, and accordingly could support thesemulti-bit coding techniques to support higher memory density. As such,the stored data states can be differentiated by either or both thedegree and the location of polarization of the ferroelectric. The useand methods of constructing an FRAM memory is covered in many recentpapers and their teaching could be applied to incorporate suchferroelectric dielectric for the 3D NOR. Such papers as by J. Muller etal. titled “Ferroelectric Hafnium Oxide Based Materials and Devices:Assessment of Current Status and Future Prospects” published in ECSJournal of Solid State Science and Technology, 4(5) N30-N35 (2015); byPatrick D. Lomenzo et al. titled “Annealing behavior of ferroelectricSi-doped HfO2 thin films” published at Thin Solid Films 615 (2016)139-144; by Uwe Schroeder et al. titled “Chapter 3, NonvolatileField-Effect Transistors Using Ferroelectric Doped HfO2 Films” publishedby Springer Science & Business Media Dordrecht 2016, B.-E. Park et al.(eds.), Ferroelectric-Gate Field Effect Transistor Memories, Topics inApplied Physics; by U. Schroeder et al. titled “Impact of field cyclingon HfO2 based non-volatile memory devices” presented at ESSDERC16; byShinji Migita titled “Thickness-Independent Behavior of Coercive Fieldin HfO2-based Ferroelectrics” presented at EDTM 2017; by Cheng, Chun-Hu,et al. titled “Low-leakage-current DRAM-like memory using aone-transistor ferroelectric MOSFET with a Hf-based gate dielectric”published in IEEE Electron Device Letters 35.1 (2014): 138-140; and byZhen Fan titled “Ferroelectric HfO2-based materials for next-generationferroelectric memories” published at JOURNAL OF ADVANCED DIELECTRICSVol. 6, No. 2 (2016); all of the forgoing are incorporated herein byreference.

Some of the ferroelectric materials could act also as a charge trappingmaterials. These two could impair each other as discussed in a paper byYurchuk, Ekaterina, et al. titled “Charge-Trapping Phenomena in HfO2-Based FeFET-Type Nonvolatile Memories,” published in IEEE Transactionson Electron Devices 63.9 (2016): 3501-3507; the forgoing is incorporatedherein by reference. On the other hand the memory cell could beengineered to have these two enhancing each other, so the ferroelectricand charge trap could be combined for enhanced memory functionality,such as presented by Yu-Chien Chiu et al. titled “Low Power IT DRAM/NVMVersatile Memory Featuring Steep Sub-60-mV/decade Operation, Fast 20-nsSpeed, and Robust 85° C.-Extrapolated 1016 Endurance” presented at 2015Symposium on VLSI Technology; Chiu, Yu-Chien, et al. “On the variabilityof threshold voltage window in gate-injection versatile memories withSub-60 mV/dec subthreshold swing and 10¹²-cycling endurance” ReliabilityPhysics Symposium (IRPS), 2016 IEEE International, IEEE, 2016; and byChia-Chi Fan et al. titled “Impact of Ferroelectric Domain Switching inNonvolatile Charge-Trapping Memory” presented at EDTM 2017; and in U.S.patent application publication 2016/0308070; all of the forgoing areincorporated herein by reference. Such enhancement is accomplished whenthe electric field generated by the charge trapping and the polarizationof ferroelectric are oriented to enhance each other.

Writing a ferroelectric memory cell techniques are provided, forexample, in U.S. Pat. No. 6,667,244, incorporated herein by reference.The following ferroelectric writing example for the 3D-NOR structurecould be also adapted to charge trap programming using FN by adaptingvoltage levels and to the above structure for which ferroelectric cellsare designed to be enhanced by charge trapping.

An example of writing conditions in the following assumes that the 4 Vdifference across the gate and the S/D is engineered to be sufficient topolarize the ferroelectric while the voltage difference below half of it(2V) is not sufficient to disturb the states of the ferroelectric.

FIG. 16A illustrates a schematic of a single cell written to the ‘0’logic state. FIG. 16B illustrates such single cell structure in asimplified cross section.

FIG. 16C illustrates a schematic of a single cell written to the ‘1’logic state. FIG. 16D illustrates such single cell structure in asimplified cross section.

The specific voltages of these structures are for illustration only andare to be defined specifically for a specific memory cell as part ofsuch memory cell engineering. In a case where the selected word-line(the gate) is shared with other cells in the array the unselected cellcould have their bit-lines (Source-lines and Drain-lines—S/D lines) atground (zero volts—0V) or in some alternatives floating. Likewise, in acase where the selected bit-line (the source and the drain—S/D lines) isshared with other cells in the array, the unselected cell could havetheir word-lines (the gate) are at ground or in some alternativefloating.

FIG. 17A-17D illustrates an alternative in which two bits are stored inone facet of the memory cell by directing the electric field only to thesource side of the memory transistor, or alternatively (not illustrated)to the drain side. This could resemble the mirror-bit concept in chargetrapping cells. This writing method could be adapted for the 3D NORfabric. The channel could be floating in the cases outlined above.

FIG. 18A illustrates a small section of a ridge of the 3D-NOR fabric.These writing schemes are driven by an electric field between thechannel, driven from the S/D lines, and the word-lines. Note that thesymbol ‘x’ in the figures represents that no writing is to be effectedat the related ferroelectric zone. For such writing techniques, the oddlevel cells are to be used while the even level memory cells could beignored. This is since in this writing technique both sides of theactive S/D are affected in the regions close to the active word-line.FIG. 18A illustrates writing ‘zero’ to a memory cell. FIG. 18Billustrates writing ‘one’ to a half of a memory cell. FIG. 18Cillustrates writing ‘one’ to a group of memory cells sharing the samebit-lines (S/D lines). FIG. 18D illustrates writing ‘zero’ to a group ofmemory cells having common word-line (gate line). These write modesillustrations are indicative of the options available for writing of aferroelectric memory option within 3D NOR structure. These could becombined with multilevel programming techniques to increase storagecapacity. Such multilevel storage is presented in a paper byMulaosmanovic, Halid, et al. titled “Switching kinetics in nanoscalehafnium oxide based ferroelectric field effect transistors,” publishedat ACS Applied Materials & Interfaces (2017), incorporated herein byreference.

These could also include multi-bit locations similar to minor bit andmulti-gates steering of bit location such as is discussed in respect toat least FIG. 10E of PCT/US16/52726 and FIG. 15A to FIG. 23 of U.S. Ser.No. 15/333,138 for further increases of memory capacity. The multistorage locations writing, is similar to that of charge trap: the sidegates could be used to modify the electric field directing the effect ofthe major gate to the selected location of the related facet. Also thetechniques presented for transferring memory, from and to high speedcells, and high density cells, could be used in respect to ferroelectricbased memory cells.

In hot-electron writing techniques the side gate steering is targetingthe channel region in which the hot electrons are being formed along thechannel width direction perpendicular to the source-drain direction. InFN and even more so for FN in which the gate is the source of thecharge, or in ferroelectric writing techniques, the steering could alsobe directed to the electric field formed in the O/N/O and/or theferroelectric regions. Accordingly it would be enough if the side gatesare positioned to affect the electric field between the primary gate andthe semiconductor region.

FIG. 18E and FIG. 18F are example illustrations how this effect might bearranged and performed. FIG. 18E is an X-Z cut-view of a small ridgeregion of a 3D NOR. It shows a section of two 1^(st) gates 1821, 1823and two 2^(nd) gates 1822, 1824. It also shows two S/D regions 1801,1803 and the channel 1802 in between them. FIG. 18F is an X-Y cut-viewat the active region of the ridge ‘marked plane’ 1805 of FIG. 18E. Itshows the side view of the channel 1802 marked channel 1832, therespective gates 1821, 1822, 1823 and the O/N/O or ferroelectric orcombination 1834. It also illustrates two memory sites that could beformed by these steering techniques. By assigning the role of main gateto 1822 and pulling the electric field by side gate 1823 and pushing theelectric field by side gate 1821 the write location could be made to1828. And, for example, by pulling the electric field by side gate 1821and pushing the electric field by side gate 1823, the write locationcould be made to be 1826. To avoid disturb to the memory related to theside gate, the side gate voltage could be set to be below the level thatcould disturb the side memory. The specific voltages could be set for aspecific memory structure and all numbers presented in here are forillustration only.

The writing techniques presented with respect to FIG. 15F, could also beused for ferroelectric based memory and the presentedcharge-trap/ferroelectric structures presented herein. In such case atleast one of the channel facets storage layer (O/N/O) could incorporateferroelectric material such as HfO₂ as presented herein before. Thewriting techniques presented in respect to FIG. 18A-18D could be adaptedaccordingly, so that the writing and erasing electric field is formedbetween the selected word-line and the selected ‘body’ while the S/Dlines are left floating, or used for electric field steering as has beendescribed herein.

An embodiment of the invention is to use such memory structures or aportion of such for Synapse-like functions. Such use of memory has beensuggested in the art for RRAM and PCM cross bar but could be applied tocharge trap or other memory types presented herein. Published work forRRAM and PCM cross bar has been by Chen, C-Y M et al. titled “Asolid-state electronic linear adaptive neuron with electricallyalterable synapses” published at Neural Networks, 1991, 1991 IEEEInternational Joint Conference on. IEEE, 1991; by Lee, Myoung-Sun, etal. titled “Implementation of Short-Term Plasticity and Long-TermPotentiation in a Synapse Using Si-Based Type of Charge-Trap Memory”published at IEEE Transactions on Electron Devices 62.2 (2015): 569-573;and by Kornijcuk, Vladimir, et al. titled “Leaky integrate-and-fireneuron circuit based on floating-gate integrator” published at Frontiersin neuroscience 10 (2016); all of the forgoing are incorporated hereinby reference.

In many of the memory structure herein the writing technique couldinclude a reduced gate voltage in conjunction with use of negativevoltages on the S/D to reduce the overall power requirements of thedevice. Such technique could also take advantage of the heterogeneousintegration of memory control circuit layer(s) disposed over a memorymatrix.

An additional inventive embodiment is an alternative for a 3Ddevice-system; such a system as is illustrated in FIG. 11E. It is toconstruct the system as array(s) of memory units, such as illustrated inFIG. 12B, and with a corresponding processor cores on top of it orunderneath. For many compute tasks the program code loaded on aprocessor core could be set according to the content loaded in itscorresponding memory unit on top or under it. Thus processing of datacould be accomplished with a short distance data transfer of less thanabout 1 mm or less than about 100 microns or even less than about 20microns, as opposed to PCB (Printed Circuit Board) based computers inwhich the data from the memory being fed though over 20 mm wires usingthe PCB. The memory unit and the processor core could be rectangular inshape with an area of less than about 4 mm², or less than about 1 mm².Alternatively, the data transfer into the 3D device-system could be setsuch that data is placed in correspondence with the designated processorto process it. An additional alternative is the use programmable logicas part of the processing logic. With the use of programmable logic, orFPGA, the logic configuration could be adapted to the data stored in thecorresponding 3D memory to further enhance processing efficiency whilereducing data movement power and delay. FIG. 19A illustrates an X-Z cutview of a 3D system in which a first strata of memory units 1902, 1904,1906, 1908, is overlaid by a second strata of memory units 1912, 1914,1916, 1918, is overlaid by a third strata of memory control circuits1922,1924,1926,1928, and is overlaid by fourth strata of processor coreunits 1932, 1934, 1936, 1938. In some embodiments, the first strata ofmemory units may be high density non-volatile memory such as Flashmemory or RRAM. In some embodiments, the second strata of memory unitmay be high-speed memory such as DRAM or static memory such as SRAM. Forexample, such computer system could be tasked to search for a personwhich meets a specific criterion. Accordingly the fourth strata corescould be set with the search in parallel in which core 1932 is accessusing memory control 1922 for that person in the data base being hold atmemory cores 1912 and 1902. In another case only one core at a time willperform the search while the other cores perform other tasks, yet thesearch is perform by a core 1932 in the data bank in 1912, 1902, andthen the search task is assigned to core 1934 which will run it for thedata in 1914, 1904 and so forth.

An additional advantage in such a 3D memory system relates to thepotential defects in semiconductor manufacturing. For example, thestructure illustrated in FIG. 19A could be processed at full reticlelevel with the expectation that some of the cores or the memory unitscould be defective and would not be activated on the end product, whichcould be designed to function with only 80% of the units functional. Assuch, the third strata of memory control circuits may have an on-chiptesting function (not shown) in order to assess the functionality of thememory layers underneath and allocate those memory blocks into theenabled and the disabled blocks, and update the data routing path(s)accordingly. An important advantage of this 3D structure is the abilityto effectively support a very fine grain of unit based construction.Such units could be designed and engineered to be sized to less thanabout 1 mm² or less than about 0.2 mm² or even less than about 0.05 mm².While the 3D system size could be larger than 100 mm² or larger than 600mm², or larger than 2,000 mm² or even larger than 10,000 mm².

Moreover, a mix of redundancy techniques could be used. As such themulti-core multi-unit 3D system of FIG. 19 could have a system controlfunction 1940 which controls the overall 3D system and could beconstructed with two strata: one strata provides redundancy to the otherat the logic cone level as been presented in U.S. Pat. No. 8,994,404,incorporated herein by reference, in respect to at least FIGS. 24A-44B.

The system control function 1940 could include input output channels toother systems, or to a communication channel such as the internet or towireless systems such as G4, G5. This could include such as fiber opticchannel, free space optical channel, wireless channel and other forms ofcommunication channels. The Monolithic 3D technology presented hereinenables heterogenous integration to enable those forms of communication.

The 3D architecture also could be useful to enable common manufacturingof a modular system that could be customized to specific needs bytechniques presented herein, such as the use of each of a continuousstructure as presented U.S. Pat. No. 8,994,404 as related to at leastFIGS. 11A-12E, FIGS. 14-17, and FIGS. 22A-23D. FIG. 19B illustrates suchcustomization. The upper portion 1952 is a magnification of section of astructure such as is illustrated in FIG. 19A, and it overlay a substrate1954. The generic wafer could be then customized by dicing it to thedesired end chip size. The dicing 1956 could be done by many of theknown techniques including conventional dicing saw, or plasma etchingalso called plasma dicing or laser assisted dicing. The dicing could bedone at designated potential dice lines 1958. These potential dice linescould include various restrictions (for example, design rulerestrictions) and support for potential future dicing including guardrings and avoiding active regions or metal lines through them.Alternatively, the dicing could be done by advanced dicing techniquessuch as laser assisted or plasma assisted dicing. And could be supportedby additional techniques to seal and provide side wall protection tosupport good functionality and reliability of the end device.

An additional inventive embodiment is an additional aspect of a 3Dcomputer system, such as is related to FIG. 19A, where there is the needto integrate multiple memory stratums to achieve a larger memory bank.In one alternative, multiple stratums could be integrated via 3Dintegration with minimum per strata processing, and then a memorycontrol stratum could be added to control each and every memory cell inthe strata underneath. These memories could be structured for suchintegrations. These memories could be volatile memory such as DRAM, NonVolatile memory such as 3D NOR, or 3D NAND or even a mix of such. In thefollowing description of such integration, it is assumed that the memoryare constructed in a same size memory unit array and each such unit iscontrolled by the same pitch of memory control lines so when one memorywafer is bonded on top of another memory wafer these memory units andtheir control lines (wordlines and bitlines) are precisely overlaid toeach other, This overlaying is subject to the wafer to wafer or die towafer misalignment precision of the bonding equipment. The integrationtechnique leverages copper to copper, hybrid or ‘fusion’ bonding inwhich the bonding process also functions as an electrical connectionprocess between these wafer/strata. Such precise bonding is presented ina paper by Kurz, Florian, et al. “High Precision Low Temperature DirectWafer Bonding Technology for Wafer-Level 3D ICs Manufacturing.” ECSTransactions 75.9 (2016): 345-353, incorporated herein by reference.Utilizing precise bonder and thin layer transfer to construct 3D genericmemory structure and integrating it with a logic wafer to form highperformance 3D compute system is presented in a paper by Zvi Or-Bachtitled “A 1,000× Improvement in Computer Systems by Bridging theProcessor Memory Gap” IEEE-S3S 2017, incorporated herein by reference.FIG. 20A-20F illustrates preparation of a wafer for such connectivityusing wafer bonding, including construction of the TLV to allow multiplestratum integration, leveraging the 3D layer transfer techniquespresented herein or other thin layer transfer techniques.

FIG. 20A illustrates a Y-Z 2000 cut view of section of a wafer, a basewafer 2002 including a SiGe “cut layer” 2001 and memory circuits 2003.

FIG. 20B illustrates the structure of FIG. 20A after etching hole region2004 substantially all the way to expose the cut layer 2001.

FIG. 20C illustrates the structure of FIG. 20B after forming top metallanding pad 2006. The isolation layer to protect the silicon sidewall ofthe memory circuit 2003 (not drawn). This top landing pad 2006 may bedrawn larger in the X and the Y direction than the pitch of a TLV asdetermined by the bonding process, in order to accommodate the waferbonding alignment tolerance of the TLV. Top landing pad 2006 may bein-plane with the silicon layer of the memory circuit 2003.

FIG. 20D illustrates the structure of FIG. 20C after covering thestructure with isolation layer 2008.

FIG. 20E illustrates the structure of FIG. 20D after addinginterconnection layer 2010 including at least one via 2014 to thelanding pad 2006. This could be a memory control line. Theinterconnection layer 2010 may be wordline, bitline and/or sourceline ofthe memory circuit 2003.

FIG. 20F illustrates the structure after adding the bottom connectionpad 2012 connected to the interconnection layer 2010.

Such prepared stratum may be bonded onto another target wafer and oncethe cut is performed the target strata is ready to have additionalstratum bonded and connected onto it.

FIG. 20G illustrates an alternative to adapted such technique to dielevel operation as was presented in reference to FIG. 4H herein. As anexample, a multilayer such as is illustrated in FIG. 4H could be used.For such the bottom layer 2042 could be silicon, and SiGe layer 2044 ontop of the silicon layer 2042, and top silicon device layer 2046. Thenusing a similar flow to the one in reference to FIG. 20A-20F herein,bottom pads 2022 and top pads 2044 could be formed. Thus themultilayered structure 2040 could be ‘cut’ and diced out and bonded at adie level onto another target wafer (not drawn), then a selective etchfrom the top could be used to first remove the silicon layer 2042 andthen thin the die all the way to the device layer, for example, byselectively etching the SiGe layer 2044. These support layers 2042 and2044 could have a thickness of about 1 micron, 1-3 microns, 3-6 micronsor even higher. The device layer 2046 itself could include sub-layerssuch as n+ and p− to support the back-bias scheme as discussed beforeherein and in incorporated references. By having the inter-stratumconnectivity structure 2022, 2024 pre-built, the stacking process couldprovide both mechanical bonding and through silicon connectivity—hybridbonding—thus simplifying the 3D system formation which could includeswafer level stacking and die level stacking yet having thin stratum inthe stack. These stratum could be at a thickness of about 10, 20, 40,100, 200, 400 nm or about one or a few microns.

FIG. 21A-21C illustrates a small region of a memory control line X-Y2100 top view. In this integration technique, a layer selected (notshown) could be used to allow multiple stratum control lines to beconnected in parallel yet by enabling the layer select only the selectedstratum could be accessed.

FIG. 21A illustrates top metal landing pads 2102 for control lines 2104such as bit line, word line, or source line that are sized to themaximum bonding misalignment margin 2101 to guarantee that the bottomconnection pad 2108 of the following stratum to be bonded will land onthe top landing pad of the prior stratum. In some of the advanced waferbonders the bonding misalignment is less than 100 nm (three sigma).

FIG. 21B illustrates the structure with the added control lines 2104 andtheir connection 2106 to the top landing pads. In many cases, thecontrol lines pitch is denser than the expected worst-case misalignmentand accordingly the landing pads are placed on multiple rows asillustrated. These control lines could be the bit-lines or theword-lines. The connectivity structure of FIG. 21A-21C assumes a controllines pitch of about 80 nm. Using an advanced lithography process,control lines pitch could be further pushed to even below 30 nm. Theconnectivity approach illustrated in FIG. 21A-21C could be adjustedaccordingly.

FIG. 21C illustrates the structure after adding the bottom connectionpads 2108. The use of the term bottom and top connecting pads is justfor the ease of explanation and being part of layer transfer process topand bottom could be flipped.

FIG. 21D illustrates the X-Z cut-view or the Y-Z cut-view 2120 of thetop landing pad during the wafer processing. Having a carrier substrate2110, the area designated for intra stratum connectivity could be firstprocessed to etch the silicon 2118 all the way to expose the SiGe layer2111 using selective etch with the SiGe as an etch stop. Silicon 2118may include a bottom layer silicon layer 2122 (dark black line) whichlater after flip bonding and ‘cut’ could become the top layer. The etchprocess could be wet or dry as the region being etched is relativelylarge, for example, of about 1 micron by 200 microns, or about 0.5microns by 300 microns. Then the region could be filled with anelectrically isolative material, for example, such as oxide 2113. Thenthe top landing pads may be patterned and then filled in with aconductive material, for example, such as copper, forming top landingpads 2112. The size of these pads 2112 could be large enough to assurethe desired electrical and physical contact after the following waferbonding step. For example, such as about 100 nm by 100 nm, or about 200nm by 200 nm, or about 220 nm by 220 nm, or about 180 nm by 180 nm, orabout 250 nm by 250 nm, or about 180 nm by 220 nm depending onproduction, design and other engineering considerations, especially thewafer bonder alignment capability. Then vias 2116 to these landing pads2112 may be formed and additional isolation 2113 could be added ifneeded. These vertical connectivity elements pads 2112 and vias 2116could be called Through Layer Via (TLV) or nano-TSV. The processing ofthese nano-TSVs could take place after the wafer has completed the hightemperature process, often called Front End of the line (‘FEOL”), whichincludes forming all the transistors, their isolation, and contacts inthe active silicon 2118. The metal pattern could include a ‘bonderalignment marks’ 2119 to support the following face-to-face precisealignment. These ‘bonder alignment marks’ could be placed at the dielevel or even at the reticle level as they are part of the full waferalignment process.

FIG. 21E illustrates the structure after completing the interconnectlayers—the Back-End of The Line (“BEOL”). The memory array interconnect2130, the nano-TSV which includes the future bottom pads 2138, thelanding pads 2132, and the vias 2136 connecting them, and the bit-linesor the word-lines 2134. An oxide 2131 could be added to cover the arrayinterconnect 2130. The process could be designed so the top surfaces ofthe future bottom pads 2138 are exposed to support the future metal tometal or hybrid bonding Such preparation could include a slight heightadjustment to ensure connectivity between the stack stratum.

FIG. 21F illustrates the resulting structure after having the structureof FIG. 21E, first structure 2144, flipped and bonded (metal to metal orhybrid bonding) to a second structure, base structure 2142 (may besimilar to first structure 2144). The base structure 2142 may not needfull nano-TSV or SiGe layer, for example, if it is supposed to be theuppermost stratum of the 3D chip; however, having a unified memory wafercould be preferred and having the ability to connect controls from bothsides could be desired.

FIG. 21G illustrates the structure after removal of the base silicon2146 of the top wafer first structure 2144. This could be done with aconventional grind followed by etch leveraging the SiGe layer 2148 as anetch stop.

FIG. 21H illustrates the structure after removal of the SiGe cut-layer2148, using selective etch to etch mostly SiGe and not silicon. Theexposed silicon layer 2122 could be oxidized to support subsequenthybrid bonding of additional structures, for example, such as firststructure 2144 on top to form a three stratum stack or as many asneeded. Alternatively, the hybrid bonding could be made of silicon tooxide and metal to metal. A few processes could be used to convert thenow top layer silicon 2122 to oxide. Such as simple etch and depositionwith potential CMP step to expose the pads, or to oxidize the topsilicon surface 2122 using low temperature techniques such as presentedin a paper by H. Kakiuchi et al titled “Formation of silicon dioxidelayers at low temperatures (150-400° C.) by atmospheric pressure plasmaoxidation of silicon” published at Science and Technology of AdvancedMaterials 8 (2007) 137-141; and by Masaki Hirayama et al titled“Low-Temperature Growth of High-Integrity Silicon Oxide Films by OxygenRadical Generated in High-Density Krypton Plasma” published at IEDM 99.Alternatively the boding could be made between the top silicon 2122 andoxide 2131 of the added stratum such as presented in a paper by R. DoBlack et al titled “Silicon and silicon dioxide thermal bonding forsilicon-on-insulator applications” published at J. Appl. Phys. 63 (81,15 Apr. 1988, all of which are incorporated herein by reference.

The process for removing the base silicon 2146 and the SiGe cut-layer2148 could include use of grinding and selective etch as previouslydiscussed. First selectively etch silicon using the SiGe layer 2148 foran etch stop, and then etching selectively the SiGe using the silicon2122 and the pads 2132 as an etch stop. Alternatively the SiGe layer2148 could be pre etched or mostly etched similar to the process inreference to FIG. 2H to FIG. 3D and FIG. 4E to FIG. 4H herein. The 3Dintegration between memory control circuits and the bitline/wordline ofthe memory array could utilize the concept illustrated in FIG. 21A-21C,as an alternative to the ‘smart-alignment’ technique such as inreference to FIG. 11F-11H, or the programmable technique of FIG.11I-11K.

FIG. 22A-22B are X-Z 2200 cut view of the stratum select connectivity.It supports a generic stratum design which could be integrated in anystack numbers of 3D integration and allow a top select of each stratum.

FIG. 22A illustrates one stratum section which is designed to support upto four stratum integrations (for example) with top access to selecteach of the stratum in the stack by the top access—SL1, SL2, SL3, SL4.

FIG. 22B illustrates a stack of four stratum 2211, 2212, 2213, 2214which are stacked so that SL1 could be used to select stratum 2211 andso forth to SL4 to select the top stratum 2214.

FIG. 22C illustrates a conventional DRAM block diagram. In the 3Dcomputer system presented in herein the memory array could be in onestrata while the control circuits, for example, such as Row Decoder,Sense Amps, Column Decoder, and Data In/Out Buffers, are placed on uppermost overlaying (or lower most underlying) strata. Such memory multiplearray stratums could be combined by techniques such as has beendescribed herein to form a larger memory 3D array. For example, the perlayer select to be added per unit array as is illustrated in FIG. 22Dfor the bitlines and as is illustrated in FIG. 22E for the wordlines. Atthe edge of the unit array the per layer bitlines—L-BLj could beselected by the control line SLi by activating select transistor 2222,which its output G-BLj is one of the control line 2104 illustrated inFIG. 21B to connected together as General Bit Line-j, as presented inrespect to FIG. 21A-21C herein. Herein the symbol i indicates the numberof the layers in the stack, and the symbol j to the count of the controllines. Similarly, at the other edge of the unit array the per layerwordlines—L-WLj could be selected by the control line SLi and itsinversion NSLi by select transistor 2224, which its output G-WLj is oneof the control lines 2104 illustrated in FIG. 21B to connected togetheras General Word Line-j, with additional transistor 2225 to deactivatethe unselected wordlines (as gate signal is preferred not to be leftfloating).

As an additional embodiment, the per layer select circuits could be madeto either the bit lines (FIG. 22D) or the wordlines (FIG. 22E) and theselect for the wordlines could be made with primarily N type transistorsfor which both the SLi and the NSLj signals could be routed from thecontrol stratum. FIG. 22F illustrates a section of such partition toarray of units illustrating a section of 3×3 units 2231-2239 along X-Ydirection 2230. Each unit may be an array of bit-cells having wordlines2242 traveling in the X direction and bit-lines 2243 traveling in the Ydirection. The memory unit array (2231-2239) size could be about 200microns×200 microns while the gap between units could be about onemicron to allow for the vertical connecting pads 2246 of FIG. 21A-21C,for the layer select 2244, 2268 of FIG. 22E for the wordlines and ofFIG. 22D for the bitlines. In the corners between units the‘layer-select’ vertical connection structure 2247 of FIG. 22A could beplaced. It should be noted that FIG. 22F like many other figures hereinis not to scale and the unit size (˜200 micron×200 micron) are not drawnin proportion to the size of gap (˜1 micron) between units, and so on.

An additional embodiment is to have two layers select circuits for eachcontrol line as is illustrated in FIG. 23A. One select sector 2314controlling the bitlines or the wordlines 2312 coming out from memoryarray unit ‘n’ 2304 before the connections pads 2316, and one selectsector 2318 after it, in between the adjacent memory array unit n+12306. The select signals pads 2317 coming from the memory controlcircuits could include two signals SLn and SLn+1. This way the verticalmemory control lines from the memory control circuits connected to thehorizontal memory control lines (Word-line or Bit-lines) via padstructure 2316 could drive each of the adjacent memory array units 2304,2306. This connectivity structure enables many use options, for example,including redundancy used to overcome defects, or multiple memory accessoptions from single units to multiple units. A 3D computer system couldleverage this flexible connectivity to blend between high speed localaccess with multiple processor cores, each accessing a local memory inparallel operation, combined with global memory access in which multipleunits are functioning as a larger memory array. The hybrid bonding ofstratum in the 3D stack allows connecting not just the active signalsbut also support signals such as ground, power and feed-through 2308 asneeded for such stratum within the stack and below and on top of it. Thespace between the memory units 2311 could be designed to accommodate thelanding pads 2316 and the layer select transistor 2314, 2318.

FIG. 23B illustrates a block diagram for the generation of per layerselect signal SLi. For example, a case in which 8 stratum of memoryarray are needed, the lower address bits A₀-A₂ could be decoded 2324 toeight layer select—SL′₀-SL′₇. In such a 3D system it could be desired touse one extra 9th stratum in which one stratum is used as redundancy toreplace a defective stratum. The operation could include first a testingcycle to check if any memory cell in a unit had a defect for which theredundancy could be used. In general, the big memory may be segmented tomany small units such as multiple thousands of units each about 200micron by 200 micron. The likelihood of two defects in two overlayingunits is extremely low so repair at the unit level could enableextremely high system yield. For memory unit by redundancy unitreplacement, the redundancy stratum may be segmented into multiple unitsaccording to the unit size of the memory stratum. For such the 8 signalsSL′₀-SL′₇ could be input to the repair control unit 2326. The repaircontrol unit will allocate the 8 layer select to the 8 good stratum outof potential 9-th stratum leaving one stratum always unselected, bygenerating the proper 9-th layer select signal SL₀-SL₈ FIG. 23Billustrates an optional a sub unit repair control by having someadditional address lines A₁₀-A₁₁ control signals to the repair controlunit 2326, so to allow different distribution of the layer select linesto the 9-th potential stratum to each quarter of the memory array. Therepair control unit 2326 could be constructed to be programmable soafter testing the arrays it could be programmed to avoid use of adefective sub array or array region. Using the enhanced access scheme ofFIG. 23A, memory stratum of adjacent unit(s) could be used as areplacement of defective unit within a stratum if needed, thereby givinga larger range of recovery options.

Persons in the memory art could adapt these techniques in manyvariations to engineer 3D Computer system with the desired memory sizewith consideration to process yield. Such could include, having firstthe logic stratum then the memory control and then overlaying the memorystack, or having the memory stack first as illustrated in FIG. 11E. The3D memory array 1131 could be a monolithic memory array or stackedmemories array such as been presented in respect to FIG. 20A-FIG. 23, orboth above and below. In such a 3D computer system it could be desiredto include a thermal isolation layer such as layer 1157 of FIG. 11E toisolate the relatively high operating temperature of the logic layerfrom the memory structure. Redundancy techniques could be also used forthe memory control circuits and the processing logic. The redundancytechnology utilized could include techniques presented herein or in theincorporated by reference art, leveraging the unit modularity aspect ofthe 3D computer system and the 3D integration in which the repair couldbe provided in a very close proximity overlaying the replaced part andpreserving the full system functionality.

In the 3D Memory stack presented herein, the unit partition could besymmetrical in which the length of the wordlines within a unit issimilar to the length of the bitlines, or the unit partition could bevery asymmetrical. These control line length and accordingly the size ofthe respective unit size in X direction or in Y direction could be about50, 100, 200, 400 micron or even one or few millimeters. The number ofconnections associated with these control lines is order of magnitudeslarger than the number of vertical connections associated with theaccess control, the per layer select (SLi). In some applications thecontrol could be broken into a few banks, each with its own select lineallowing more control flexibility to individual memory banks within theunit. Such could allow better granularity for redundancy use or parallelaccess to the unit memory array. These banks could be allocatedhorizontally (X, Y) or vertically (Z). Such could also be used forparallel access from logic overlaying and or logic underlying the array.Such could also allow for sections of the memory array to be mapped forglobal access across multiple units. Such variation and the supportcontrol logic to support them are known in the art and could be designedby an artisan in computer architecture and memory controls.

FIG. 24A illustrates an alternative 3D computer system utilizing thetechnologies presented herein. The base 2410 is a carrier substratewhich is also provides cooling to the main multi cores computing stratum2424, through a first thermal isolation layer 2426 the computer stratumis connected to the multi-unit memory control stratum 2428, whichcontrols the multi-unit memory array strata 2430. Overlaying the memorystrata is a second memory control stratum 2432 which provides secondaccess to the same memory strata 2430. Through a second thermalisolation layer 2434 a second computing stratum 2436 could be connectedto the second memory control stratum 2432. The second computing stratum2436 could communicate with external devices utilizing a communicationstratum 2438. The communication stratum 2438 could utilize wired,wireless, optical or other communication channels to communicate withexternal devices. An upper heat removal apparatus could overlay thecommunication stratum 2438.

An additional alternative is to integrate in such 3D computing structureactive cooling. Such active cooling work was recently supported by DARPAand the report on these techniques is presented in a paper by Chainer,Timothy J., et al. “Improving Data Center Energy Efficiency WithAdvanced Thermal Management.” IEEE Transactions on Components, Packagingand Manufacturing Technology (2017), incorporated herein by reference.Such active cooling could be incorporated in addition or as replacementof the thermal isolations 2426, 2434. FIG. 24C illustrated a 3Dstructure with active thermal cooling supporting feed through ofelectrical interconnects 2472 and thermal vias 2474.

Herein the term layer transfer or layer cut could be applied to use ofSiGe as a cut layer either as sacrificial layer with far different etchrate vs. silicon as presented such as in reference to FIG. 2A-FIG. 3D,or as an etch stop layer for back grinding and silicon etch scheme.Either one of these techniques could be used for the 3D system presentedherein.

Additionally, alternative structures to SiGe could be used for theformation of the ‘cut layer’. In some embodiments, the ‘cut layer’ mayalso function as an etch stop layer or sacrificial layer which could beselectively removed. Such alternatives have been detailed in PCT/USpatent application 16/52726 and U.S. application Ser. No. 15/333,138,incorporated herein by reference. For example, one may use a highlydoped layer of N+ or P+ or porous layers. A unique advantage of a dopedlayer used as ‘cut layer’ is the ability to make it at the processingfab as part of the conventional process flow via conventional processessuch as ion implantation or in-situ doped epitaxial growth. Anotheraspect is the ease to make the ‘cut layer’ selectively using patterningwhich opens up more options; for example, instead of a full layer or toallow change in the layer thickness in different location across thewafer. The use of a doped layer as a ‘cut layer’ could be combined withother functions, such as a back bias connection for transistors or otherdevices. The choice of ‘cut’ between undercut and lift off or grind andetch back could be in consideration of the type of etch and itsselectivity in respect to choice of the ‘cut layer’ structure.

Many other variations of 3D system could be constructed utilizingtechniques presented herein or in incorporated by references. In someapplications, the peripherals circuit could be placed on more than onestratum. This could be used for memory partitioning to small units suchthat the area of a unit is too small to fit all the require memorycontrol on a single stratum. For example, the upper most stratum may becontrol logic to control about the upper half of memory stratums whilethe lower most stratum may be control logic to control about the lowerhalf of the memory stratums.

Another approach that could leverage such monolithic 3D technology ismultiple port access to the memory array. This could also includenon-symmetrical multiport access, such as one access port could accesssingle unit, while another access port could access multiple units. Thismultiport non-symmetrical access could be achieved by controlling theaccess to the segments of word-lines and/or bit-lines. The access fromthe top and the access from the bottom could be independent, yetsynchronized. In such, for example, the wordlines and bitlines could beaccessed by per unit memory control from the top control stratum, whilethe bottom control stratum provides access to the same wordlines andbitlines with multiple units control, providing one memory port accessper unit from the top, while the bottom control stratum could provideaccess to a block of memory that could include multiple units.

The 3D memory architectures herein constructed with arrays of memoryunits each comprising memory strata in which every stratum has at leastone select controlled from the overlaying and/or underlying memorycontrol stratum, and the multiple options opened up by such architectureincluding yield repair, local and global access, is applicable to manymemory technologies, including volatile and non-volatile. Thesearchitectures benefits are applicable to many of the 3D integrationtechniques presented herein including epitaxial based with sharedlithography and layer stacking with grind and etch-back. A technologistin the art of memory systems could engineer a specific system leveragingthe techniques presented herein.

FIG. 24B illustrates a generic 3D memory structure “G3DM” which could beconstructed according to the techniques presented herein. Such a 3Dmemory could include a controller to manage the memory including selftest and advanced refresh techniques. The 3D memory could include atleast one or two stratum of memory control circuits, first memorycontrol stratum 2448 and second memory control stratum 2452 and the 3Dmemory stack 2450. The 3D memory stack 2450 structure could beconstructed and may include an array of memory units each with its ownmemory control structure as a tile of the 3D structure, it could alsoinclude 3D memory array structures such as 3D NOR or 3D NOR-P disclosedherein or elsewhere. It could be provided as a wafer ready to haveadditional customer specific circuits, for example, such as control andencryption, which could be similar to those presented in FIG. 24A 2436,2438. And it could be constructed on top of a ‘cut-layer’ so it could becut over other structures. These additional integration steps could bedone at a die level after dicing, or at a wafer level to be dicedafterwards. Dicing afterward could be performed by: conventional sawdicing, laser assisted dicing, or etch assisted dicing. The structurecould be useful to support more than one device size as previouslypresented forming a continuous structure which could be tiled tospecific device size(s) near the final phase of the processing, thusallowing stocking of generic wafers, etc. The external surfaces such as2454 could include the pads for the additional custom circuits tointerface with. Alternatively, such external surfaces with the pads maybe used for subsequent conventional chip packaging. The decodingcircuits could be part of the generic 3D memory structure “G3DM” such aspart of the memory control circuit 2448 or 2452, and accordingly thenumber of wires per such memory unit (about 200μ×200μ) connectivity withthe customer specific circuits could be at the range of 30-100. Suchconnectivity could be readily achieved with today's face to face bondingcapabilities. The G3DM could incorporate self test to invoke redundancymemory stratum per unit at product release and also during normaloperation to extend operations with self-repair capabilities. The G3DMcould also includes wireless test and report capabilities as discussedsuch as in U.S. Pat. No. 9,142,553 in reference to at least FIG. 24A-Cand FIG. 48-FIG. 50. The system level memory structure herein could beused for many types of memory technologies and products. A very commonmemory technology is DRAM for which additional enhancements could beintegrated in such high granularity memory structures. DRAM is known torequire refresh with the common refresh cycle of about every 60 ms. Therefresh rate is known to be driven by the worst case of relatively fewmemory cells that exhibit high leakage. Recent works have suggestedadaptive refresh to reduce the refresh energy by adapting the refresh tothose sections that require higher refresh rate while reducing therefresh rate for most of the device's cells. Such as presented in papersby Ahn, Jin-Hong, et al. titled “Adaptive self refresh scheme forbattery operated high-density mobile DRAM applications,” published inSolid-State Circuits Conference, 2006. ASSCC 2006. IEEE Asian. IEEE,2006; and by Mukundan, Janani, et al. titled “Understanding andmitigating refresh overheads in high-density DDR4 DRAM systems,”published at ACM SIGARCH Computer Architecture News. Vol. 41. No. 3.ACM, 2013, all incorporated herein by reference. The high granularity ofthis 3D structure with arrays of relatively small sized units couldenable deploying such techniques at the unit level, or even at a layerof a unit, so the refresh rate could be reduced to units that eitherhave not be written into yet, or that exhibit lower leakage. Inaddition, for a unit in which all the memory layers are good, the choiceof the unit to be left unused could be based on refresh needs. Thepartition to units with the associated reduction of the word-lines andbit—lines length could itself reduce leakage and accordingly therequired lower refresh rate. Alternatively these techniques could enablethe reduction of the DRAM capacitor size for some application whichcould enable significant overall memory cell size reductions.

Memory centric applications such as intelligent systems or searchapplications could be implemented as a memory focused processing systemutilizing such 3D systems as is illustrated in FIG. 24A. In such asystem, a new approach could be used, instead of the conventionalprocessor centric approach in which data is transferred to and from thecentral processing unit, transfer the process to where the data is. Asan example, the dashed border 2462 of FIG. 24A may represent a databasestored in the memory 2430 associated with people in city A while thedashed line 2464 indicates data bank stored in the array 2430 associatedwith people in city B. And if a search is needed in respect to city Athe program performing the search could be transferred to the processingunit in the logic layer 2436 located in the area marked by 2462, whilethe program code related to a search in city B could be transferred tothe processing core located in the region marked by 2464. Memory centricsystem operations could leverage the 3D computer system illustratedherein as a new compute paradigm. The program or code itself could alsobe stored in the memory matrix 2430. Additional option is to runparallel processing on the memory stored in the memory matrix 2430converting it from one form to another form. There are many form of datatransfer such as from amplitude domain to frequency domain as oftencalled Fourier Transform. Another type of transform is to form multiplefeature plans with one or very few bits from a many bit per data pointrepresentation, which is useful for technique for brain inspiredalgorithm.

Another alternative for constructing a 3D memory stacked structure is toreduce changes in the memory wafer processing and compensate by addingprocess steps to the stacking process. FIG. 25A illustrates structure2500 as alternative in respect to the structure of FIG. 21E. A wafersubstrate 2501 with cut-layer 2502, memory semiconductor structure 2504,memory interconnection structure 2506 and oxide layer 2508 may beformed. The in-between units control line 2510, through memory via 2536and connecting pads 2538 are formed similar to those of FIG. 21E. Thedifference is that the in-between silicon 2505 is not etched away butrather shallow trench isolation 2512 and bottom dummy contacts 2514 areadded, using conventional memory processing. The bottom dummy contact2514 may be formed at the same step as the source and drain region ofmemory bit cell formation. The bottom dummy contact may be an n+diffusion region. The through memory vias 2536 are connected to therespective bottom contacts 2514. FIG. 25B illustrates this alternativein respect to FIG. 21H after having a structure such as 2500 flipped andbonded to similar structure 2508, and have it substrate and cut layerremoved, thus shown as processed bonded layer 2506. Then, vias 2582could be opened by removing silicon 2505 to expose the bottom side ofthe bottom contacts 2514 as is illustrated in FIG. 25C. If the STI 2512of the standard process are not deep enough, then the via formationprocess could include the STI locations to etch through to assure fullisolations of the vertical connection from the substrate and each other,thus forming full etch structures 2583. Alternatively, the silicon atthe regions could be first be etched out and replaced with isolationmaterial. Then add landing pads 2522 on top of bottom contact 2514 as isillustrated in FIG. 25D, to prepare the structure for the followinglayer.

An additional step could be added which is forming alignment marks forthis stacking process. The bonding alignment mark could be included inthe metal layer as the bonder could see these alignment marks from thetop view of the wafer. FIG. 25E illustrates the structure of FIG. 25Awith alignment marks 2532 utilizing the STI process. These marks couldbe used once the wafer has been flipped and the substrate and the cutlayer have been removed. Other alternatives could be the use of an ionimplant process or leveraging the contact process for the alignmentmarks.

Additional steps that could be taken in the memory fab to help thefollowing stacking process could include using a lithographicallydefined doping process. FIG. 25F illustrates an optional use of N+doping for extending the contacts 2514 into the silicon with conductiveN+ silicon 2534 reducing the need of forming the metal connectionsillustrated in FIG. 25C-25D 2502, 2522. Such N+ doping can beaccomplished by adding extra high dose deep ion implantation in thememory wafer fab or even attainable using a part of a standard processstep. The depth of N+ layer may be the substantially close to the bodythickness of the stratum to be transferred, so that N+ regions play asnano-TSVs. FIG. 25G illustrates an optional use of N type silicon as thecut-layer 2540, and leaving the regions 2536 for the nano-TSV as P−.Once flipped and bonded, the process of substrate removal using the N asetch stop could allow etching these P− regions 2536 exposing thecontacts 2514. Filling with conductive metal and then removing theexcess using processes such as CMP would make the stack ready for thenext stratum. As discussed previously, the selective etch of P siliconto N silicon could be an anodizing process which would first etch the Psilicon to become porous and then the porous silicon could beselectively etched away. Utilizing these techniques the memory arraywafer could be processed using a standard memory process or such withsimple changes, and then stacked using simple processes that could bejust bond, grind and etch, or with some additional steps as presentedherein.

As a general note, the use of top pad and bottom pads herein areexchangeable as with the use of layer transfer techniques. Thesestructures could be flipped for specific applications using thepresented technology and structures herein. In some cases there might bea need to flip the layer before bonding it to the target wafer. Acarrier wafer, such as presented in at least U.S. Pat. No. 8,273,610,incorporated herein by reference, could be used to support suchflipping. The carrier wafer could also leverage techniques presentedherein in respect to the term “cut layer”, and could be designed to begrind and etched out, or to be reused having it ‘refurbished’ and usedagain. Additional techniques for such a carrier wafer, could be to forma porous layer at the top of a carrier, such as presented in respect tothe ELTRAN process, without the need for the epitaxial step but ratherjust use it with silicon top or add oxide for the bonding. Anotheroption is to use a wafer with thick oxide and/or a nitride cover of afew microns and optionally add grooves at the dice lane or betweenlithographic projection fields. Then detach the carrier wafer by athough-side etch leveraging the very high selectivity of etch ratesbetween silicon and oxide or nitride. An additional alternative is toimplant ions such as a combination of helium and hydrogen and then uselow temperature (˜400° C.) ion-cut for detach. An example for a need offlipping is in a case when the desired landing pads 2006 are in a rangeof about 200×200 nm² or about 400×400 nm² while the designated locationfor these pads might be desired for operating silicon. In such case avia smaller than 100×100 nm² through the transferred silicon film(strata) could be used and the landing pads could be constructed overthe carrier wafer, once the layer was transferred onto the carrierwafer.

An additional enhancement could be by adding to through-strata-via thatwe could also call a through-layer-via ‘TLV” such as illustrated in FIG.20H including top landing pad 2054, a via or chain of vias 2050, and abottom connection pad 2052. Such connection path might serve as paththrough without connecting to other elements within the strata it ispassing through. It could allow signal paths through such as connectingsignals between first memory control stratum 2448, of FIG. 24B, andsecond memory control stratum 2452 without connecting to any elementwithin the 3D memory stack 2450. Furthermore, a plurality of dummy viasnot connecting any pad may be included to improve process uniformity,serve as mechanical support, or in some application when it is desiredfacilitate heat dissipation, such as thermal pipes and paths to anexternal surface of the device.

An example for such a feed-through TLV is illustrated in FIG. 24A. Abase wafer carrying, for example, processors and other circuits 2410,2424, could be sourced from conventional 2D fabrication process andfacility. It could include connecting pads on its upper surface. Then awafer carrying multilayer memory strata 2430 with its memory controlcircuits 2428 could be bonded on top of the sourced wafer forming theconnection between the standard flow wafer and the stack memory andcontrol circuits. Then using the feed-through TLV connections could bemade with the upper stratum 2436 which could include the I/O circuits tointerface the 3D system with external devices. These could also includewired connections such as, for example, pads, balls or pins, or wirelesssystems such as electromagnetic, optical, etc. This heterogeneousintegration supports the use of different device crystalline material,RF, Analog and other forms of heterogeneous integration. Such couldinclude magnetic films using technique such as presented in U.S. Pat.Nos. 9,337,251, 9,357,650, 9,357,651, 9,647,053, 9,679,958, incorporatedherein by reference. These ferromagnetic films could be added toconstruct an on-chip inductor using standard metallization layer(s) withhigh quality factor for voltage regulators or RF transceiver/receiver toimprove the 3D system effectiveness and capability.

A standard wafer fabrication technology or baseline technology could beestablished for the memory per unit pin out position and function. Thatstandard wafer fabrication technology or baseline technology could alsobe used for the custom logic design so it could integrate the genericmemory wafer presented herein, for example, by bonding. Each standardwafer could include alignment marks for the custom logic top layer tohelp align the generic memory wafer during the bonding process. Thestandard wafer could include processing cores compatible with the sizeof the memory unit such as, for example, about 200 μm by 200 μm, astreet width between units such as, for example, about 1 μm. The signalsto be connected in-between such as: 40 pins for address, 16 pins fordata, 10 pins for control (such as read and write) and 4 pins for passthrough paths. Some of these pins could be defined in the industrystandard as expansion options or to allow more than one memory type orarchitecture. With about 100 pins per unit, the area for each pin couldbe about 20 μm by 20 μm, which allows the use of most wafer bondersavailable currently in the industry. Additionally, the generic memoryand control stack could be designed to be about 50 μm thick so it couldbe shipped, handled, and bonded by industry standard processes andmachines. Such could become also a standard for which the memory stackcould include a path-through the interface layer with the properthickness so the total stack would be about 50 μm thick. For example,for a 16 memory layer stack of 1 μm each and control stratum with I/Ostratum of 2 μm, the stack thickness could be about 18 μm, and apath-through layer of about 32 μm could be bonded on top to bring theoverall stack thickness to about 50 μm thick, compatible with thecurrent industry capability. The pass through paths could be built usingtechnology such as TSV to pass, for example, the approximately 100signals from the generic memory to the custom 2D processor device, tothe processor device such as based on planar, SOI, FinFET, orgate-all-around technology.

FIG. 29A illustrates such ‘pass-through add-on structure’ 2902constructed within a silicon wafer substrate, having base substrate2910, designated cutline 2908 that could be formed by cut-line techniquepresented herein or just by timing the grinding and etch once bonded asit design to be many microns thick. The ‘pass-through add-on structure’could include pre-built isolated TSV 2904 to function as the conductivefeed through. An enhancement of such ‘pass-through add-on structure’ isto have it function also as a thermal isolation between the heatgenerating processor and the memory stack, for example, as isillustrated in FIG. 29B. The enhanced ‘pass-through add-on structure’2912 could have some of the silicon 2906 be replaced by etch, depositionand planarization with thermal isolating material 2917 such as siliconoxide. With feed-through TSV 2914 and the remainder of the siliconsubstrate 2916 similar to those illustrated in FIG. 29A. Those‘pass-through’ structures could be reserved for the arbitrary purposethat can be determined later by the system designer. The stratacontaining ‘pass-through’ structures may be a generic product such asmemory, sensor, power or communication chip. Alternatively, use of suchfeed-throughs could be, from the processor logic in the logic layer2424, to the I/O layer 2438 to connect to an I/O or analog functionbeing placed on the 2438 layer, or to interconnect memory control layerbeing placed on top 2432 and under 2428 the memory structure 2430. Suchcould be used to coordinate use of the redundancy control functionbetween the top control 2432 and under control 2428. An additional usecould be to coordinate dual control to support multiport access to thesame memory matrix.

The technique of using a precise bonder with staggered pads onword-lines or bit-lines presented in respect to FIG. 21A-21C, could beused to add memory control logic over 3D memory such as 3D NAND or 3DNOR. This could be an alternative to the technique presented here inrespect to FIG. 11F-11K and FIG. 12F-12J. An advantage of a staggeredpads approach could be the parallel processing of the memory and memorycontrol which then could be integrated into a 3D device by bonding.

The stacking techniques presented in respect to FIG. 20A-FIG. 25G, andFIG. 29A-29B could be extended to 3D memory such as 3D NOR. Such couldinclude stacking multiple strata of 3D NOR each having multiple layersof memory. In such case, the per layer select transistors of FIG.22D-FIG. 22E could become per memory strata select. This per layerselect transistors could be implemented within a control stratum on topor below the multilayer memory strata or alternatively without suchcontrol stratum but rather in the memory structure such as by doublingthe ridge select transistors to have to serial transistors instead ofthe one ridge select transistor (such as 1213, 1222, 1332). In suchcase, one transistor could function as the ridge select while the othercould be globally controlled by the per layer select signal SLi,effectively providing strata select to support simple vertical stacking.This could allow use of the same memory control circuits to controlmultiple strata with relatively simple additional control and z-decodingcircuit to control the strata select signals. Such stacking couldinclude periodical stratum of rebuffering and redrive to support therelevant control lines. FIG. 26H illustrates an X-Y 2690 top view ofsuch added transistor for forming Strata-Select SS1 2692, SS2 2694. FIG.26H is a portion of FIG. 12E with the added transistors 2692, 2694, 2696to function as global strata select for such stacking of 3D memorystructures. In such case the stacking flow presented in respect to FIG.21A-24B could be adapted for stacking of 3D memory strata such as 3DNOR. The 3D memory strata could be designed with units such as presentedin respect to FIG. 22F. These units could be structured similar to the3D memory units such as presented in respect to FIG. 12D. Each such unitcould be designed to have the wordline access both from the top and thebottom and each of those word lines could include stacking pads arrangedsuch as presented in respect to FIG. 21B. The bit-lines could also bestructured to be access from the top and bottom and to have landing padstructures similar to FIG. 21B. And similar pad structures could beadded to the ridge selects. For the Strata Select, the pad structurecould be designed similar to the structure of FIG. 22A.

Additional option is to stack different memory type. Clearly stackingcould include many type of stratum, yet the unique aspect of thestacking technique in here is to form vertical connection of theword-lines and the bit-lines while having per strata select line such asSLi of FIG. 22D-22E. These word-lines and the bit-lines could controlplurality of memory type including volatile and non-volatile. Sharingthese memory control lines could allow efficient form of memorystructure and in some cases, could even allow direct data transfer fromone memory type to another memory while keeping some of these controlline unchanged reducing power for such data transfer and reducing timefor such transfer.

An additional step that could be included in the preparation of 3Dmemory structures for stacking is adding bonder alignment marks. Precisebonders generally need alignment marks to align wafer to wafer Thesealignment marks could be incorporated in the proper location on the topand/or bottom layers of the 3D memory wafer structure using a propermask of the 3D memory structure such as in a nonfunctioning zone overthe wafer such as in-between memory structures.

The technology for precise wafer bonding is being enhanced, recentlydemonstrating the improvement of wafer to wafer alignment tolerance from200 nm three sigma to 100 nm three sigma, and efforts are underway todevelop bonding precision to 50 nm. These works have been reported bypapers such as by Peng, Lan, et al. “W2 W permanent stacking for 3Dsystem integration.” Electronics Packaging Technology Conference (EPTC),2014 IEEE 16th. IEEE, 2014; by Sakuma, Katsuyuki, et al. “Bondingtechnologies for chip level and wafer level 3D integration.” ElectronicComponents and Technology Conference (ECTC), 2014 IEEE 64th. IEEE, 2014;by Sugaya, Isao, et al. “Precision wafer bonding process for futurecost-effective 3DICs.” Advanced Semiconductor Manufacturing Conference(ASML), 2015 26th Annual SEMI. IEEE, 2015; and by Kurz, Florian, et al.“High Precision Low Temperature Direct Wafer Bonding Technology forWafer-Level 3D ICs Manufacturing.” ECS Transactions 75.9 (2016):345-353, all of the forgoing are incorporated herein by reference.Herein we presented at least two stacking flows, one using‘Smart-Alignment’ techniques as presented in reference to at least FIG.11F-FIG. 12J, and one utilizing ‘Hybrid’ and/or ‘Fusion’ as presented inrespect to at least FIG. 20A-FIG. 23B. The fusion bonding techniquesenable a simple stacking operation as it could be done without the needto form vias in the transferred layer thereby reducing the need forlithography, metal deposition, and processing per stack layer at thestacking fab. But for such fusion bonding based stacking, the landingpads as illustrated in FIG. 21A are required. In some applications, itmight be effective to mix these stacking techniques for the formation of3D structure such as, for example, the one illustrated in FIG. 24B. Anexample for such could be to use fusion bonding for the stacking of thememory stratum as related to FIG. 21A-FIG. 23A, and use‘Smart-Alignment’ for connecting the memory control strata 2428(providing the decoding, sense amplifiers and other memory control).Precise bonders could align the wafers being stacked but could notovercome die level misalignment within these wafers. It is relativelyeasier to control the die level alignment for wafers processed in thesame processing fab line using the same stepper, or matched steppers.The memory stratum could be processed in the same line as they areproviding the same circuits. The control stratum would be processed in adifferent process and might be harder to achieve the same die to diemisalignment as the memory stratum. By using ‘Smart-Alignment’ for it,the landing pads could be exchanged to landing strips as illustrated inFIG. 11G and could allow a larger overall misalignment between thecontrol stratum and the memory stratum. Such hybrid stacking could keepa tight space between units of the memory stratum with landing pads, asan example, 200 nm×200 nm, while the connection of the control stratumto the memory stack could use landing strips of 300 nm length (and lessthan 80 nm width) to accommodate the additional die level misalignmentbetween the control stratum and the memory stratum.

An additional option to accommodate large total stacking misalignment isto build the relatively larger landing pads and pins over the memoryunit. This way the space 2311 between the memory units could be keptrelatively small while the landing pads could be made large enough toaccommodate the total error which could include the bonder alignmenterror or/and the die placement errors. Such over the array padsconstruction could add costs associated with the processing of such overthe array pads and additional per stacking layer costs in the stackingfabs to build these extra layers of landing pins. FIG. 25H-25J couldillustrate such over the array connectivity structures. FIG. 25H islower portion 2560 is similar to FIG. 25A. The upper portion 2561illustrates the landing pads 2550 constructed over the memory bit cellarray 2556. These landing pads are connected to the respective bit-lineor word-line by via 2552, connection wire 2554, and via 2562. Theseadditional metal layers are added on top of the isolation covering thearray 2558 and are with the additional isolation material 2557. It mightbe desired to have two versions of over the array pads: one with landingpads 2550 and one with landing pins 2570 as illustrated in the lowerpart of FIG. 25I. FIG. 25I illustrates bonding a such wafer with largelanding pads 2550 on top of another such wafer with landing pins 2570.FIG. 25J illustrates the structure after removal of the top substrateand SiGe layer and constructing landing pins 2572 or alternatively largelanding pads (not drawn) for the following stacking step. Artisans inthe art could mix and match this alternative stacking option to thespecific 3D system design.

The 3D memory stack herein enables stacking multilayers of memorystratum in which the vertical connectivity is at the word-line andbit-line level. Such 3D stacking enables use of a memory control formultiple memory stratums thus reducing cost in addition to benefits inperformance and power reduction. Yet vertical connectivity at theword-line/bit-line level could be a technology challenge as the highpitch of these memory control lines may prevent the use of techniquessuch as ‘smart-alignment’ as there might not be enough room to run TLVsthrough. For such cases the Hybrid/Fusion bonding techniques presentedherein, at least in respect to FIG. 21A-FIG. 25J, are an effectivetechnique to provide word-line/bit-line level 3D connectivity.

The 3D memory stacking presented herein could be modified to accommodatetechnology limitations or cost objectives. Such modification couldinclude connecting only the bitlines at the unit level while connectingthe wordlines at a far courser granularity or vice versa (connecting thewordlines at the unit level and the bitline at the bank on multiple unitlevel). Other modifications could include staggering the layer selecttransistors position of FIG. 22D or FIG. 22E, to accommodate the highmetal pitch of the respected control lines. Another modification couldbe to position the connecting pads for/on odd control lines in one sideof the unit and for/on even control lines on the other side of the unitthereby resembling the structure illustrated in FIG. 12C-12E.

An additional alternative to a form buried cuttable layer is to replacethe buried SiGe with oxide, nitride or other layers. This could be donefollowing a step of isotropic etch as been described such as inreference to FIG. 2I. This could use deposition techniques such as ALDor other conformal deposition techniques to refill the etched-out spacewith a proper dielectric material. This could be done while forming andkeeping posts to hold the top silicon layer or in two steps; firstportion and then additional etch and replace the remaining portion.Following the replacement an epitaxial process could be used to seal theentrance holes 224. This could be done for the whole wafer or atselective sections for specific applications. This could be done as partof forming a generic substrate or per a specific application. Thereplacement could be done for specific circuit considerations, forexample, such as substrate capacitance, or back bias, or back gate. Thiscould also be done to support any of the 3D integration flows such aspresented herein for which the replacement material could be lateretched with a much higher selectivity. For example the selectivity ofdry etch of nitride vs. silicon could be set to be 2,000:1, which ismuch higher than the selectivity of SiGe vs. silicon. This could also bedone in combination with bonding to another substrate and detaching witha finishing process such as residue etch CMP and epitaxial. This flowcould also be done as an alternative process for the formation of SOIsubstrates, and may have lower cost to manufacture compared to thecurrent methods. This could also be done using a stain etching toconvert the SiGe layer to porous layer as previously presented herein.

An additional alternative for a ‘cut-layer’ is to use a single atomlayer of Graphene as presented in a paper by Kim, Jeehwan, et al.,“Principle of direct van der Waals epitaxy of single-crystalline filmson epitaxial graphene.” Nature communications 5 (2014); and Yunjo Kim,et al., “Remote epitaxy through graphene enables two-dimensionalmaterial-based layer transfer” published at NATURE|VOL 544|20 Apr. 2017,incorporated herein by reference. It was discovered that a single atomlayer of graphene being placed on a single crystal substrate could allowa single crystal epitaxial growth on top having the base crystalorientation and quality. Yet the layer grown on top of the graphenecould be pulled off as the graphene layer has “weak van der Waalsinteractions, and which also allows facile layer release from 2Dsurfaces”. Enabling “the grown single-crystalline films are rapidlyreleased from the graphene-coated substrate and perform as well asconventionally prepared films”. Accordingly, such a single atom graphenelayer could serve as alternative to the porous layers described hereinor combined with such or other forms of ‘cut-layer’ presented herein.The base substrate could be reused after ‘cutting’ off the functionallayer. A graphene cut could be used in a similar way to the originalconcept of porous layer for formation of SOI wafer as was named ELTRANby Cannon.

Many mix and match of these cutting techniques could be utilized fordifferent product formation and related flows. One such mix could beused for die to wafer 3D integrations as discussed in U.S. patentapplication Ser. Nos. 15/095,187 and 15/173,686 and herein. So, the cutof the 6 microns thick die could use the graphene as the cut layer butthen the following a step of thinning the layer after being bonded tothe target wafer, and could leverage the SiGe etch selectivity for etchand controlled thinning to below 1 micron to allow a simple process withnano-TSV through (with less than 400 nm via diameter) the thinned die.

Additional technique that could be used for a 2D material such asGraphene as a ‘cut layer’ is an oxide type post that could be etched outprior to the layer transfer step. As the substrate with a cut layerbeing built in could go through the full front end of the lineprocessing and some back of the line processing before the layertransfer, it could be desired to add in such posts to keep the stabilityof the structure for the various processing steps prior to the transferstep. Using a modified STI step, holes could be etched all the waythrough the graphene into the underlaying substrate, and filled withoxide. These holes could be made in the dice lanes. Then as one of thelast step before performing the layer transfer operation these oxideposts could be etched away releasing their hold. Additionally, these inthe dice lanes could be extended to a full dice lane etch so that in thelayer transfer step each die may be peeled off independently from theother dies.

The release process could include a polymer or other material such asnickel to help form a stress which together with temperature, such asliquid nitrogen or less than 400° C. degree spike heating, could helpthe detach and release of the re-useable substrate from the 3D structurecomprising the target wafer and the bonded transferred layer. Analternative technique could include the use of pulling 5-30 micron thinlayers off reusable wafers using a technique called controlled spallingsuch as presented in papers by Shahrjerdi, Davood, and Stephen W.Bedell. “Extremely flexible nanoscale ultrathin body silicon integratedcircuits on plastic.” Nano letters 13.1 (2012): 315-320; and by Bedell,Stephen W., et al. “Layer transfer by controlled spalling” Journal ofPhysics D: Applied Physics 46.15 (2013): 152002; and U.S. Pat. Nos.9,698,039, 9,704,736 and 9,713,250, incorporated herein by reference. Areusable “cuttable” substrate could be constructed using the followingsteps; 1) Form the thin layer with desired silicon thickness on top of aSiGe etch stop layer using an epitaxial process over a donor wafer. 2)Form a reusable carrier by growing 3-10 micron thick oxide (or nitride)over a silicon wafer. 3) By using controlled spalling pull out 5-10micron layer off the silicon over SiGe (top Si/buried SiGe/fracturedbulk Si stack) from the donor wafer and bond it on top of the reusablecarrier, thus forming the reusable “cuttable” substrate. Optionally, thefractured surface portion of bulk Si maybe treated to be planarized forbetter bonding to the reusable carrier. The reusable “cuttable”substrate could now be processed with building the desired circuits ontop of it. Than it could be bonded on top of a target wafer. Then usingselective oxide or nitride etch from the side of the wafer, the bulk ofthe reusable “cuttable” substrate could be detached leaving over thetarget wafer the circuits and the layers previously being bonded to the3-10 micron thick oxide. Than using SiGe as an etch stop the 5-10 micronsilicon could selectively etched followed by a SiGe etch. In the processthe edge of the wafer could include protection of the interconnectlayers to protect them from the side oxide detaching etch.

The ‘cut-layer’ technology presented herein could also be used forapplications requiring a very thin device. An example of suchapplication is integrating a semiconductor device in a contact lens orin application requiring a very flexible circuit layer. In theseapplications the ability to use a standard semiconductor fabricationprocess following by thinning the device thickness to a few microns orhundreds of nano-meters or even less, could be key enabling technology.

An additional inventive embodiment for a 3D memory constructed of arraysof relatively small memory units, with the memory control circuits ontop or under of such memory units relate to the ability to perform perunit refresh and other techniques to extend memory effectiveness. Thiscould be applied for DRAM type memory as presented herein before andalso for non-volatile memory such as charge trap, floating gate andferro-electric based memory. These memory units could have an Xdirection and/or Y direction size of a few tens of microns, or a fewhundreds of microns. For example, some of the general concerns withmemory structures relate to disturb and other forms of losing memoryfidelity. These could impact the level of memory density utilization.With such a 3D memory system as illustrated in FIG. 19A, the controlsystem could copy the contents of a memory unit to cache storage, erasethe unit and re-write the content to restore memory fidelity. Theserefresh cycles could be performed based on time or activity of thatmemory unit. These refresh operations could be performed at a time thereis no active use of the memory so auto-maintenance could be performed.FIG. 27 illustrates a block diagram for such a refresh operation flow.Such a refresh could extend the effectiveness of the memory by enablinga greater number of bit site locations with the memory cell and agreater number of storage levels within such storage sites.

An alternative to form the 3D NOR fabric illustrated in FIG. 3A-3B andFIG. 4A-FIG. 10D of PCT/US16/52726 is to use the “punch and plug”technique, commonly used in current 3D NAND formation. FIG. 26Aillustrates a top XY 2600 view of holes 2608, 2609 formed in amultilayer structure such as is illustrated in FIG. 3A ofPCT/US16/52726. The multilayer structure may be the stack of multiplesingle crystalline N+/P/N+ semiconductors layers. The multilayerstructure may further include silicon for N+ layer (designated for thesource and drain S/D) and SiGe for P layer (designated for thechannels). Alternatively, the SiGe region may serve as S/D while Si mayserve as the channel material. The memory transistor may be constructedfor single crystalline vertical channels and single crystallinehorizontal bit lines as presented in reference to FIG. 4A-FIG. 10D ofPCT/US16/52726. Herein, the term “punch” represents a deep etch processto make a hole deep through multiple stack of layers while “plug”denotes a deposition process that either substantially fills the punchhole or partially fills it, such as a layer or layers deposition on theinner sidewall of the punch hole. The holes are usually punchedsubstantially all the way through the multilayer structure. The holescould be formed in horizontal rows 2602, 2604, 2606 which could functionsimilar to the valleys 308 in FIG. 3B of PCT/US16/52726. After thevertical anisotropic etch forming the holes, an isotropic etch could beused to extend the holes to slightly overlap as is illustrated in FIG.26B. Alternatively the holes could be formed directly as illustrated inFIG. 26B. Then using deposition, such as ALD, the O/N/O layers 2628,2629 could be deposited in the holes, similar to as is done in 3D NAND,as illustrated in FIG. 26C. The gap opened by the overlaps 2618, 2619between the neighboring punch holes, could be designed so, thedeposition of the O/N/O layers would close it, by having the properO/N/O thickness, forming rows of isolated holes, 2622, 2624, 2626, withisolated ridge 2623, 2625 which function similar to the ridges 309 inFIG. 3B of PCT/US16/52726. Such auto-shutting of the gaps enables forthe subsequent gate formation to be self-aligned, reducing a lithographystep for the gate patterning. Then the inside of the holes could befilled with gate material 2630 which could be polysilicon, tungsten oralternative gate material or combination of such. The O/N/O stackthickness is usually more than 10 nm and less than 30 nm, andaccordingly the gap between the holes 2619, 2629 could be designed to beless than 20 nm to assure isolation between the gates of adjacent holes.FIG. 26D illustrates having the gates along the same column in Ydirection connected by global wordlines 2632, 2634. The holes of evenrows 2604 could be phased from the holes on odd rows 2602, 2606, tosimplify the wordlines connections, to enable individual selection ofeach storage facet as an alternative to the connectivity in FIG. 5A or5B or 5E or 8A of PCT/US16/52726. Most of the variation and enhancementpresented in the PCT/US16/52726 could be adapted and implemented withsuch “punch and plug” process. For example, the indentation presented inrespect to FIG. 10B of PCT/US16/52726, could implemented by having ‘odd’holes 2608 larger than ‘even’ holes 2609. Furthermore, the formed ridges2623, 2625 could be sliced with slits (‘valleys’) to expose the sidewallof multilayer structure and selectively expose the bitlines—S/D regionfor silicidation and so forth as explained in reference to FIG. 8 ofPCT/US16/52726. An artisan in memory technology would be able to adaptmany of the technology alternatives presented in PCT/US16/52726 inrespect to a straight lines ridge in valleys to the punch holesformation of ridge and valleys as illustrated in reference to FIG. 26B.

An additional advantage of the punch holes technique illustrated in FIG.26A-26C is the ability to use the adjacent wordline to steer storagelocation. So, for example, when writing using WLn the adjacent wordlineWLn+1 could be used to pull the charge toward it or to push charge awayresembling the concept presented in PCT/US16/52726 in respect to FIG.10B and FIG. 10E. Accordingly using both WLn−1 and WLn+1 could extendthe storage capacity when writing using WLn.

An alternative process could include sealing some holes such as the‘even’ holes 2509, then plugging the ‘odd’ holes 2508 with O/N/O andgates, then remove the sealing and optionally isotropic etching theunplugged ‘even’ holes 2509. Such selective sealing process is oftenused for the in-situ sealing process to create a vacuum cavity in MEMStechnology by using very low step coverage deposition process or verynon-conformal deposition process, causing voids. In order to protect themultilayer structure by some residual sidewall deposition of the sealingmaterial, a dummy mask pattern on the very top of the multilayerstructure may be incorporated. In this approach, the holes to be sealedfirst have a substantially smaller diameter than the holes to be pluggedfirst. Holes sealing could be done by processing such as presented inU.S. patent application Ser. No. 12/979,592, incorporated herein byreference.

FIG. 26E is a top view X-Y illustration to show the use of the singlehole punch process to construct the various elements which may be neededfor the 3D NOR fabric. The region cut is illustrated by the dash line2660 and the in picture cut 2662 is to indicate that the structure couldinclude many more memory cells in the X direction. The structureresembles the structure of FIG. 12D. The ledger could be read asfollows, the un-punched multilayer structure 2640 forming the inbitlines ridge select transistor 2642 and in-silicon layer transistor2644 used as part of the per layer programming (PE1-9 of FIG. 28),1^(st) gate pillar 2646, 2 ^(nd) gate pillar 2648, control gate 2650 ofthe in-silicon transistor for ridge select and PE gate, a verticalpillar for ground 2652 for all layers (2800 of FIG. 28), programmablegate 2654 for the PE transistors, isolation pillars 2656, contactpillars 2658 for per layer contacts (L1-L4, 2812-2818), optionalfeed-through pillars 2639 which could be used to transfer signals fromthe upper side of the fabric to the bottom side. The processing of theseholes could be done for each function while the other holes are sealedor by other alternative techniques presented herein. Processing thesepunch holes together saves processing cost because in 3D memorystructures the holes punch process through the multi-layers structure isa slow and expensive process. In many cases the holes diameter is about100 nm or smaller yet the multilayer structure could be of a few micronsthick.

An additional advantage of simultaneous holes punching is having theseholes self-aligned in the vertical direction enabling dense structuresas illustrated in FIG. 26A-26E. FIG. 26F and FIG. 26G are side cut viewsalong X-Z direction 2670 to illustrates the difference between holesetch together/simultaneously (FIG. 26F) vs. holes punch in twoindependent etch steps (FIG. 26G). The self-aligned holes 2674, 2676,2678 in a multilayer structure 2672 could be used for differentfunctions as illustrated in FIG. 26E. FIG. 26G illustrates holes etchedinto a multilayer structure 2682 in which holes 2684, 2688 are etched inone step while holes 2686 in another step. With ‘Single Punch’ thesidewall vertical scallop pattern of the etched hole is substantiallythe same as the sidewall vertical scallop pattern of the other holesetched at the same time, being processed at the same process into auniform structure. The peak and valley pattern of the scallop iscontinuous along the X-Y direction between these simultaneously etchedholes.

A known challenge in 3D memory formation relates to the etch aspectratio for the holes punching process. At the current state of etchtechnology it is about 1:60 which imply that for multilayer substrateswith 3 microns thickness the smallest consistently attainable hole wouldbe about 50 nm diameter. To keep the holes diameter small for thickermultilayer substrates the following techniques could be applied. A layertransfer technique could be used to punch holes from both sides of themultilayer substrate enabling about double the multilayer thickness. Andsuccessive holes punching, followed by epitaxial growth of thesubstrate, could be applied to construct a thin hole in a thickmultilayer structure.

An additional alternative that could be combined with many of the 3D-NORstructures presented herein and in at least PCT/US16/52726 could be touse the ridge split process to replace the SiGe portion with metal tofunction as the S/D and having the Silicon portion function as thechannel. For example, in respect to FIG. 41E of PCT/US16/52726, insteadof a partial SiGe etch perform a full SiGe etch and then either use athin oxide first or just perform conformal deposition of metal to befollowed by an etch removing the metal from the side walls and leavingit as replacement of the SiGe regions, thus functioning as S/D. For suchalternative, the silicon region should be kept un-doped or P− doped tofunction as the 3D NOR channel regions. At the edge of the ridge theproper adjustment should be made in forming the staircase access. Theseadjustments could include replacement of region of the metallic S/D withp type silicon for the formation of the ridge select. Alternatively anepitaxial step of N+ type silicon could be used to form the S/D. Anadditional step of etching the ridge split again could be used to cleanthe slit from the epitaxial over growth and reduce the risk of leakagebetween S/D lines. Additionally the epitaxial step could be engineeredto only partially fill the space formed by the SiGe removal, followed byadding metal as described above, combining both techniques to replacethe SiGe forming the S/D. An additional aspect that could be integratedin the 3D NOR formation is to use a high work-function metal for thewordlines to reduce punch-through leakage risks. Persons in the memoryart could adapt this alternative to the various relevant structures ofthe 3D NOR memories presented herein.

The 3D integration technique such as presented in respect to FIG. 1 toFIG. 6D herein could be used to support many derivatives of memoryproducts by a mix and match of memory control circuits on top or belowthe memory array. These could allow multiple control circuits, some thatuse multi-bits per cell and some that do not, and also the manytechniques of multi bit presented herein. The memory array could also bemade with a generic size which could then be customized for a specificmemory product by properly designing the memory control circuit andsizing the end product by the placement and setting of the dicing lines.

An additional inventive embodiment to enhance 3D memories is to use analternative per layer access by sidewall strapping throughone-time-programmable anti-fuse to the method and structure presented inreference to FIG. 43 of PCT/US2016/052726, or by similar multipleprogrammable connections such as is used for RRAM and Bridge-RAM. FIG.28 is a modified structure to support this alternative method. L1, L2,L3, L4, (2812, 2814, 2816, 2818) are the vertical contact pillars toserve as per layer access. Each one of these contact pillars could beprogrammed to connect to a Bit-Line (BL1-BL4) by breaking a thin oxide(OTP), which could be considered an anti-fuse between it and theBit-Line (2841, 2842, 2843, 2844). The Bitlines and/or pillars could beengineered to provide a more stable anti-fuse providing an ohmicconnection when linked; for example, by include a high concentration ofatomically large lattice atoms, such as Arsenic in silicon, which wouldbe incorporated into the link when fused. The pillar maybe formed usingpolysilicon with the same doping polarity of BL to provide an ohmicanti-fuse. The connection region could include the horizontal‘programming-enable-transistors’ PE1-PE9 controlled by gate pillar 2803having a contact 2832 PE, which provides controlled connection to thevertical grounding pillar 2801 with ground contact 2800 GND. Thehorizontal transistors PE1-PE9 are embedded in the Bitline using asimilar technique presented herein for the ridge select transistors.These transistors comprise charge trap so they could be programmed to bedisconnected. The programming could be performed by the memory controlcircuit 2850 using the Vpp Gen to generate programming voltage and ‘PEnable’ to enable the programming, as follows:

-   -   1. Initially, all PEs (PE1-PE9) are erased (to low Vt) to pass        ground potential to their respective BLs (BL1-BL9).    -   2. Vpp is set to a high enough voltage to break the ‘anti-fuse’        made of the thin oxide (OTP), than P1 is activated presenting        the programming voltage on L1. Then ‘P Enable’ activates the        gate PE opening up all the horizontal programming enabling        transistors (PE1-PE9), connecting all the Bitlines to ground.        One of the anti-fuses would break which would connect L1 to one        of the Bitlines (randomly). Let say (for example) BL1 is        connected to L1. Then the programming voltage drops as the        current through the activated anti-fuse pull the voltage on L1        down enough so no more anti-fuses would break. A soak algorithm        could also be initiated to make the anti-fused link more stable.    -   3. Then Vpp and PE could be set to program PE transistor (to        high Vt) connected to the randomly fused BL in step 1 to stop        passing ground voltage. In this case, PE1 transistor is        programmed to high Vt. Now, only the rest of the PEs excluding        PE1 could be passing ground potential when PE is activated.    -   4. After P1 is disabled, P2 is enabled and the cycle repeated        creating connection between L2 and random BL.    -   5. Repeat step 2 to 4 for rest of BLs.        The selection of which Bitline would be fused first could be        guided by changing the vertical pillar ground connection 2801        from metallic pillar to resistive pillar-like poly silicon which        could give advantage to the upper Bitline closest to the GND to        fuse first. This concept of random (or guided) selective fusing        by parallel access to multiple anti-fuses is been implemented        for random number generator as is detailed in a paper by Chuang,        K-H., et al., “Physically unclonable function using CMOS        breakdown position,” International Reliability Physics Symposium        (IRPS), 2017 IEEE International, IEEE, 2017, incorporated herein        by reference. During this programming of per layer connection,        all the relevant ridge selects could be disabled to reduce the        risk of sneak paths. The per layer connection technique        presented in respect to FIG. 28 could be combined with the per        layer connection technique presented in respect to FIG. 43 of        PCT/US2016/052726 to various alternatives of mix and matched by        an artisan in the art.

It will also be appreciated by persons of ordinary skill in the art thatthe invention is not limited to what has been particularly shown anddescribed hereinabove. For example, the use of SiGe as the designatedsacrificial layer or etch stop layer could be replaced by compatiblematerial or combination of other material including additive materialsto SiGe like carbon or various doping materials such as boron or othervariations. And for example, drawings or illustrations may not show norp wells for clarity in illustration. Further, any transferred layer ordonor substrate or wafer preparation illustrated or discussed herein mayinclude one or more undoped regions or layers of semiconductor material.Further, transferred layer or layers may have regions of STI or othertransistor elements within it or on it when transferred. Rather, thescope of the invention includes combinations and sub-combinations of thevarious features described hereinabove as well as modifications andvariations which would occur to such skilled persons upon reading theforegoing description. Thus, the invention is to be limited only byappended claims (if any).

We claim:
 1. A method to construct a 3D system, the method comprising:providing a base wafer; transferring a first memory wafer on top of saidbase wafer; thinning said first memory wafer, thus forming a thin firstmemory wafer; transferring a second memory wafer on top of said thinfirst memory wafer; thinning said second memory wafer, thus forming athin second memory wafer; and transferring a memory control wafer on topof said thin second memory wafer; wherein said transferring a memorycontrol wafer comprises bonding of said memory control wafer to saidthin second memory wafer, and wherein said bonding comprises oxide tooxide and conductor to conductor bonding.
 2. The method according toclaim 1, wherein said first memory wafer comprises a cut-layer, andwherein said thinning of said first memory wafer comprises a finalthickness of said thin first memory wafer of less than 20 microns andgreater than 0.1 microns.
 3. The method according to claim 1, furthercomprising: forming a logic stratum disposed either above or below saidthin first memory wafer; and forming a thermal isolation layer disposedbetween said logic stratum and said thin first memory wafer, whereinsaid thermal isolation layer is designed so during said 3D systemoperation a first temperature of memory cells of said thin first memorywafer is at least 20° C. lower than a second temperature of said logicstratum.
 4. The method according to claim 1, further comprising:thinning said memory control wafer.
 5. The method according to claim 1,wherein said transferring a second memory wafer comprises bonding ofsaid second memory wafer to said thin first memory wafer, and whereinsaid bonding comprises oxide to oxide and conductor to conductorbonding.
 6. The method according to claim 1, further comprising:performing a step of memory test, wherein said thin first memory wafercomprises a first memory, and wherein said thin second memory wafercomprises a second memory; and then performing a step using a firstportion of said first memory as an alternative for a portion of saidsecond memory or a portion of said second memory as an alternative for asecond portion of said first memory.
 7. The method according to claim 1,further comprising: performing a step of dicing said base wafer, saidthin first memory wafer, said thin second memory wafer, and said memorycontrol wafer, wherein said dicing results in at least one die having aplanner size greater than 40×40 mm².
 8. A method to construct a 3Dsystem, the method comprising: providing a base wafer; processing amemory control circuit on top of said base wafer; transferring a firstmemory wafer on top of said memory control circuit; thinning said firstmemory wafer, thus forming a thin first memory wafer; transferring asecond memory wafer on top of said thin first memory wafer; and thinningsaid second memory wafer, thus forming a thin second memory wafer;wherein said transferring said second memory wafer comprises bonding ofsaid second memory wafer to said thin first memory wafer, and whereinsaid bonding comprises oxide to oxide and conductor to conductorbonding.
 9. The method according to claim 8, wherein said first memorywafer comprises a cut-layer, and wherein said thinning of said firstmemory wafer comprises a final thickness of said thin first memory waferof less than 20 microns and greater than 0.8 microns.
 10. The methodaccording to claim 8, further comprising: forming a logic stratumdisposed either above or below said thin first memory wafer; and forminga thermal isolation layer disposed between said logic stratum and saidthin first memory wafer, wherein said thermal isolation layer isdesigned so during said 3D system operation a first temperature ofmemory cells of said thin first memory wafer is at least 20° C. lowerthan a second temperature of said logic stratum.
 11. The methodaccording to claim 8, further comprising: transferring a memory controlwafer on top of said base wafer.
 12. The method according to claim 8,wherein said transferring said first memory wafer comprises bonding ofsaid first memory wafer to said memory control circuit, and wherein saidbonding comprise oxide to oxide and conductor to conductor bonding. 13.The method according to claim 8, further comprising: performing a stepof memory test, wherein said thin first memory wafer comprises a firstmemory, and wherein said thin second memory wafer comprises a secondmemory; and then performing a step using a first portion of said firstmemory as an alternative for a portion of said second memory or aportion of said second memory as an alternative for a second portion ofsaid first memory.
 14. The method according to claim 8, furthercomprising: performing a step of dicing said base wafer, said thin firstmemory wafer, and said thin second memory wafer, wherein said dicingresults in at least one die having a planner size greater than 40×40mm².
 15. A method to construct a 3D system, the method comprising:providing a base wafer; processing a memory control circuit on top ofsaid base wafer; transferring a first memory level on top of said memorycontrol circuit; thinning said first memory level, thus forming a thinfirst memory level; transferring a second memory level on top of saidthin first memory level; thinning said second memory level, thus forminga thin second memory level; wherein said transferring said second memorylevel comprises bonding of said second memory level to said thin firstmemory level, and wherein said bonding comprises oxide to oxide andconductor to conductor bonding.
 16. The method according to claim 15,wherein said first memory level comprises a cut-layer, and wherein saidthinning of said first memory level comprises a final thickness of saidthin first memory level of less than 20 microns and greater than 0.8microns.
 17. The method according to claim 15, further comprising:forming a logic stratum disposed either above or below said thin firstmemory level; and forming a thermal isolation layer disposed betweensaid logic stratum and said thin first memory level, wherein saidthermal isolation layer is designed so during said 3D system operation afirst temperature of memory cells of said first memory level is at least20° C. lower than a second temperature of said logic stratum.
 18. Themethod according to claim 15, wherein transferring a first memory levelcomprises bonding of said first thin memory level to said memory controlcircuit; and wherein said bonding comprises oxide to oxide and conductorto conductor bonding.
 19. The method according to claim 15, furthercomprising: performing a step of memory test, wherein said thin firstmemory level comprises a first memory, and wherein said second thinmemory level comprises a second memory; and then performing a step usinga first portion of said first memory as an alternative for a portion ofsaid second memory or a portion of said second memory as an alternativefor a second portion of said first memory.
 20. The method according toclaim 15, further comprising: performing a step of dicing said basewafer, wherein said dicing results in at least one die having a plannersize greater than 40×40 mm².